A bike getting shaky at 50kmh is a major red flag.
Are your wheels balanced, are you tyres mounted on properly?
If it's not that, but because of the frame, then I'd be crying.
For screws that loosen like bottle cage ones, use loctite. Loctite goes there, as well as on chaining bolts, and depending on your crankset, on crank arm bolts. And on derailleur bolts. And on garmin mount bolts.

Well at least noting else disintegrated!
This one should last a while longer.

Fair enough. As for the SL7—well, the SL8 is noticeably more comfortable to ride, so in that respect, you could say the X68 has more in common with the SL7.

Like I said, it’s a good frame so far. I’m actually surprised—surprised enough that it made me raise an eyebrow!
But let’s be clear: it’s not an SL8. The SL8 offers a smoother, more refined ride, as I’ve mentioned. I’m no expert, but even doing something as basic as the tap test on the down tube and top tube, they sound different. Not very scientific, I know, but it says something.

In terms of stiffness, the X68 is right up there—even the bars feel solid. This bike is definitely planted, not a noodle.

Five years ago, I wouldn’t have gone near a copy or fake frame, but they’ve come a long way—very close now.
It’s a bit like the 1:1 Rolex clones—experts now need loupes and specialised equipment just to spot the fakes. That’s how close these frames are getting. Manufacturers will have to step up to stay ahead.

I rode the SL8 yesterday using the same wheels — it’s the only set I have at the moment.
As I mentioned, the SL8 feels more refined and smoother, which is clearly down to the carbon layup. It definitely has an edge, though whether that edge is worth the extra £4,000+ is debatable.

That said, it was only a single 50 km ride, so I’ll need a few more rides over the next few weeks to really see how it holds up.

This is just my personal opinion — I’m just one guy, not an expert if people want to listen and it helps great.

The X68, it’s a good frame however people have had quality problems and that fork issue was not good but I will obviously keep a close eye on
If TanTan (or whoever actually makes it) put a bit more time and care into the quality and finish, I’d happily pay an extra $150–$200 myself.

Before considering sizing down the frame, it might be worth checking a few setup-related things first. One common cause of numb hands is shifter/hood positioning - if they're angled too far upwards, it can put your wrists in an early position and lead to pressure/numbness. Try rotating them slightly down so your wrists stay in a more neutral position when on the hoods.

Bar width and reach/stem length can also be factors. A shorter or more upright setup can help reduce pressure on the hands. You could also look into padded bar tape or even gloves with better cushioning if you're not already using them.

A smaller frame might help if you're really stretched out, but I'd tweak the cockpit setup first - it's usually a quicker and cheaper fix.

Hope that helps!