Singular Osprey & Genesis Equilibrium: winter road bike build

Reading ^ up there about squirming front end thing...

I notice you're on Deda RHM01 44cm bars? I've recently fitted them (42cm version) to my winter bike and they've certainly got a lot more flex then the FSA Vero(?) 40cm bars on my summer bike. I'm not sure if that would contribute to the issue.

No, I resolved that, it was the tyre pressures being too high. Particularly on greasy winter roads. The bars don't seem too flexy to me. The whole front end seems more than stiff enough, actually.