Yes I have noticed serious performance issues but it’s hard to say if it’s related to windowed mode or not..
I’ve just changed my runner in Lutris to wine-10.8-staging-x86_64 and the fixed window issue thus far hasn’t occurred.
Possibly not an option if you use steam however and you may need to do what this post says Lutris Javacript Error
Still need to evaluate if this is better for performance though, will have to update next time I multibox in a fleet.