A further update for those that might find this via search...

Changed down to a Salsa Poco 38cm bar a few months after getting the 40s. I got the 40s as 38 seemed too narrow, but I think the jump from 44 to 38 was just too much in one go, even if 38 was the right size.

Handling is fine on 38s having ridden 40s for some time, even triathlon cyclocross dismounts which I expected to problematic weren't. I have them paired with fiz:k bar gel, really comfy on the hoods, corners and drops. Done about 800km on them now.

The only consideration I'd note is with clip-on aerobars there isn't a lot of room up front. And it took careful setup to get a good aero position and not have my arms catch on the elbow pads while in the drops. I have the Profile Design T2+ with their aerobridge addon (not the short DL ones).

However the current aero position is comfortable and my fitter is happy the biomechanics, so it is possible with 38s.

M.