Thanks guys!
It's funny how you can overthink things. I had never considered that my fronts may be too small. The rears are 17x8.5 with 255s and some other e90 owners have seen good results from another pair of rears with 255s on the front. This might be a good option so I'm going to swap fronts and rears for a few days and make sure everything clears.
I do also think I may have hit the limit of the rs4s but the next step up is a lot more pricey.
The front bar is not adjustable so I'll leave that for now.
Diff is a single spinner unfortunately 🙁
@bcozican car is an 06 330i. M3 front arms (-1.5 camber), Whiteline front and rear bars, Whiteline rear subframe inserts (seem to really only add nvh), Bilstein shocks and eibach Springs.