In a 38 cm bars I have both an Ergonova alloy and a LTD. Huge difference in stiffness. It actually seems that the flex comes right at the stem clamp, and the LTD actually deforms right there -- not in a passive state but when flexed by riding. The alloy Team version simply doesn't flex. It's as hard as the toughest track sprint bars (Scatto and Easton EC90 track sprint bars) that we've been using. So picking your bar wisely will give you a lot of stiffness you can't recover with your choice of bar.
Beyond that, the stems seem not to flex that much, but actually torque on the steer. We had both Enve 1.0 and 2.0 forks, so hopefully construction and other issues are equivalent except for a weight difference which shows up mostly in the wall thickness of the steer (and it's quite a significant difference). with both forks mounted in the identical frame with identical headset and spacers, we looked at flex and saw a big (huge) difference with either fork -- either fork simply distorted the top of the steer. We tried using a longer steer with 2 cm spacers over it just to see if this was a problem at the end of the steer, and we had some improvement, but even 2 cm from the end of the steer, the thinner steer still deformed from any stem we put on it. You didn't have to be a rocket scientist -- you could see it right in the opening of the stem clamp.
As for reliability, we kept seeing problems with Deda Zero hardware and galling and breaking problems with any titanium hardware. 3T was better than some (Deda was the worst) at Ti hardware, but I don't think you'd want to keep the Ti hardware. How much weight are you saving? How much will extensive gauze bandages weigh?
Alloy bars are heavier these days because they were breaking too much with ultralight wall thicknesses and European standards required more durability. It's not a lot of weight (20-30 grams), but it makes them hugely stiffer. Frankly, I'd go with a slightly stiffer steer, alloy bars, and alloy stem, and save the weight elsewhere. If stiffness doesn't matter, the lighter steer and lighter bars seem perfectly durable, and you won't save weight going to carbon so it's either a cosmetic issue for you or simply stick with the nice alloy ones and just avoid the few that have reliability or recognized flex problems. You won't have a problem with 3T or Enve in those regards.
Can you give us more details on all of these tests? How was the Thomson X2 compared to X4?
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Froome.GramzFailed Custom Bike