As I mentioned out next set will most likely be 275s square setup (as it's basically impossible to get a staggered set in 18s and I'm not buying new rims already have two sets of 18s).
That said above is before/after comparison of the front if you go to 275 square.
2.8% bigger means your speedo will be a good amount more accurate.
At 75 on the dash you'll be going 74 vs. 72. (also it won't read wrong "low" until 107
The ability to rotate tires and the fact you are willing to trade cornering for comfort, I think you'd be very happy with a square setup on 275s.
It should definitely feel different but prob no more different than my e53 with sport suspension and wife's e70 without. We both have 255/55/18 and she has the 50i which begs the question: if BMW put 315s on the 4.8 WTF putting 255s on the 50i! (The tires break free at pretty much every shift at full throttle). The rear tires are wearing much faster than the front. Even when we bump up to 275s I expect that to happen why I don't want to switch to stagger setup.
I just realized the caveat in your case. You may have staggered rims!
If you have 9/10 rims which is not uncommon, you can't really rotate and means might as well use a staggered set.