The use of regular flaps with regular ailerons actually gives the wing washout. And works like gangbusters. I've used that on big gliders and didn't see any huge difference in how slow the sucker got before the ailerons got mushy compared to landings without the flaps deployed. So my thought is that with flaps down, ailerons don't lose effectiveness more than they do at the same airspeeds with the flaps up. It's the speed that matters. And you can go slower with flaps.

As for flaperons-with-flaps............ Only flew a couple of big birds with flaperons and didn't see anything to like. Didn't need a bit more drag than standard flaps give. And that's about all flaperons can give you that I could see in practice.

It was described to me that flaperons with flaps should be a positive. The new profile of the outboard wing when flaperons are activated has a new stall angle and it matches the new stall angle of the inner wing with it's flaps down, matches it better. Darned if it looked to me like that mattered. At least in practice, landing the suckers. There might be a benefit for big gliders with partial deployment of both when you're thermalling hard. That part of the envelope pays you back if you can suddenly create more camber on demand. And more camber outboard is just as good as inboard.