So basically, if the head tube notch is 2.5 cm, the gain in handlebar height compared to a traditional stem on a frame without a head tube notch is 10mm....is that right?

I am not sure exactly what you mean. I think first, it is easier to just substract 2.5 cm to the geometry chart advertised stack. Stem/handlebar vertical stack is an independant matter regardless of the frame geometry.
So to keep things simple, I separate the frame geometry from the cockpit setup.

A standard stem has a 40 mm clamp height, but with a 125 mm / -9° setup, the downward angle drops the effective rise (measured from the top of the handlebar where your hands rest) so it acts more like a 20 mm stack above the spacers.

The Avenger Y-bar has a lower 25 mm clamp height, but its positive rise pushes the total height up to 55 mm (top of handlebar, where your hands rest).

My Winspace T1550 gen 2(size large) had a 560 mm stack +40 mm spacers + 125 mm stem at -9 (20 mm vertical rise) =620 mm at top of handlebar. Same fit would be Avenger size 56 ( 565 mm stack according to the chart, but in reality it is 540 mm due to the notch) + 25 mm spacers + 120 mm stem(55 mm vertical rise)=620 mm at top of handlebar. Both gives me the same effective stack at top of handlebars. I ignore headtube angle because difference are marginal and it simplifies explanation.

Okay, so my build is finished. Just quick update from my perspective. I build the bike myself, like the others and previous Avenger Shuttle SL. I'm having Tagoola Pulse 50UL and 1x12 SRAM AXS with Force shifters and the rest is RED. As I will probably use XMCS crank, I bought the tripeak 3 in 1 BB. In general, i had no issues with cables, or with BB or screws, or honestly with any element of the frameset. Assembling was pretty easy and fast, I did all based on the R8-RS user manual. Only one elements is missing in the user manual, the screws and elements that holds the upper bearing or I haven't seen it. The routing with the Y bar was a pleasure and there is only one way of going thru. Those two pieces are very easy to connect. Top cap is pretty funny and with unusual shape. I'm wondering if 4 Nm and enough for handlebar and fixing screws. I will check and verify that on the ride today. I didn't encountered any issue with the headset play. I used 4 Nm for the top cap as adviced. No information what should be the tightening power for the handlebar and stem. Seatpost and clamp the same, no issue, Nm as in the manual. I didn't cut the seatpost. For the axles a used 10 Nm at the moment. I used 4 cm of spacers so 8 of them, not looks very bad, of course without any of them is the best. However, as I mentioned previously, after calculation I have the same level as on my shuttle. For me the comfort is the most important, I will survive how it looks.

I will prepare some reel and post on my instagram of course.

For now the weight is less than 7 kg in size 58, with pedals, bottle cages, garmin and varia mount.

Hi Marius, did you try the bike? Loose headset happens after a big ride with torque/sprints, did you try that?

Thanks! I emailed them what i wanted. Cost a extra 150 Usd.
Piano black gloss and brushed gold decals.

Hi yall,
so I had headset play for 1 year. Tryed little 0.25 mm C-shims  as suggested here and also tryed better and longer expander plug (DEDA) without any success. I decided to buy  a different Compression C-ring  on aliexpress(see picture). Now it works perfectly. I chose the 7.3 mm but maybe the 6.3 mm could have been ok too. Just dont use the C-ring provided with the frame. Chris from Velobuild discarded the issue saying the issue with previous frame was solved few years ago despite many people on this forum with similar issue. I can confirm the new C-ring provided by velobuild with this frameset is not really better. Too stiff maybe.

Anyhow, problem solved and can finally ride the bike!

Have a bit of time on the TX setup now. overall it's... acceptable, I guess.  I mean, it works.  It has some annoyances though.  Minor leaking on both caliper pistons as previously reported.  I'm sure WT would replace them, but I don't feel like pulling them off and waiting a couple weeks if I am being honest (the whole "send it in then we will ship the replacement") is a big turnoff.  Levers rattle a bit at times, as others have noted.  Rear bleed port is in an awkward spot, imo - hard to get fittings aligned when installing or bleeded, etc.

I constantly fight the ch-ch-ch when shifting.  New (when TX installed) Ultegra cassette, new DuraAce/XT 12sp waxed chain.  It's a bit maddening, because it doesn't happen every time, but more often than not.  Adjusting it out is almost impossible, or at least to me it is - since it doesn't occur on every shift.  So you think you might have it adjusted out, then it starts happening again.  I've checked the hanger alignment, played with all kinds of B-screw clearances, reset initial setting and of course played with manual tuning to my wits end.  When I get it as good as I can get it, I will still have some chatter in the middle of the cassette.  It's truly maddening, tbh.  Enough so that combined with the leakly pistons and rattling levers, I am considering just upgrading to DI2.  Could repurpose this kit on my Gravel bike, or just sell it outright I suppose.

Maybe I should try that goldix cassette first, though.  Just odd that higher end Ultegra cassette would be the issue.  TBH I never heard of Goldix before the above poster mentioned it.

OH - Also Cade Media/Wild Things just did a test/review on the Rotor-branded Wheeltop kit, and thoroughly trashed it.  Many of the issues they dealt with are common issues discussed here and on FB groups, so in reality it just appears they stuck the Rotor name on the TZ group with some minor aesthetic changes...  Having trouble posting the link, just search Cade Media on youtube it will be one of the recent vids...

Which caliper you use? There are 3 wheeltop models..thanks

i have noticed there is quite a lot of play in the fd when its on the lower chainring, is anyone elses like that? on the outer the cage is solid but on the inner position you can wiggle it around and worse even at its most inner position there is a tiny bit of chain rub on the 2 largest sprockets but you can manually move the cage in by pressing it enough to remove any rub

Yup same issue here. Did not solve the problem yet. I will swap for a grx with wider chainline to cheat this... Some peole on forum also noted that issue. No idea why other people sont face this issue though

Hi, recently? i seem to have most recent app and firmware.