What kind of riding are you doing?
As I get older, I know I would prefer a FS bike.
An overall, good frame would be the 057....the 256 will be lighter and is getting way more common and preferred.
If you like the fit and feel of your cross bike....you should probably take the measurements and compare them the many Chiners....there is a list or two of them on here.

Not that you asked but couldn't cut much weight off that.  I see one big area.
Since you are going for light weight and you are an XC racer....you could save over a 80g dropping the shimano rotors and going windcutters or quaxar iris(138g for both)
Otherwise, you could save maybe 40g on your seat.
You could go for Extralite or ?escapes me to save nearly a 100g on your thru-axles.
30g? or so with a starnut
Others would be minute after that.
I guess the obvious would be the fork for biggest savings - you could get into the 17lbs.
Very cool build...you going to make it more personal with any design/coloring or such?

My biggest concern is the amount put in it....with material(sterling silver) and cost.
Not sure how they attach, but as someone mentioned the headtube is concave and tapered
Sure hate to have that drop off.

Heck, the thru-axles aren't necesarily a weight penalty if you spend some cash....Extralite
But, much like many like the ease of XT brakes....their weight penalty is overlooked also.

Surely, stiffness is improved just from more material 12mm vs 9 or 10mm...same with bb30
Now, is it any of us can register....seriously doubt it.

Sjon7283 - not to ruin your day but at Merlincycles.com - in UK
You can get the 987s for US $290(strength of US dollar and they have 10% still off) - quite a bit less - not sure about other costs if you aren't in the US
and they are great brakes...they will work for most riding styles but for XC perfect.
The only difference from the new M9000 race brakes is the piston material....the new phenolic piston can supposedly resist heat 10% better.

Interesting seat choice...don't think I've seen that used....will be interesting to hear your thoughts on it.

I have the 987s from Merlincycles in UK - best prices especially with strength of dollar and needing to get rid of them for the M9000 line.
Mine came moto.  I removed cable from handle put tape over and ran it up the 057 frame.  Some have put a small nail/screw in to cap off...that is fine if you are cutting your brake lines after running them through your frame because of the displacement.  I was able to reverse the moto and run cables through the frame and not have to bleed.
Like all Shimano's these are grabby(but not as bad as trails with servo-wave) but I have gotten used to them and get good control from them. 

You need the 'campy' size.
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