FWIW, there is
no way anyone who has mounted 22" wheels on their 300C isn't taking a noticeable, if not significant, performance hit...unless of course they happened to invest in light-weight, 3-piece forged wheels at $1500 a pop.
I ran across a program some time ago that did a fair job estimating effective HP loss/gain relative to changes in unspring weight. It was very enlightening. I will try to dig it up again. It more or less convinced me that unless I'm prepared to spend big $$$ on forged modular wheels, the payoff in style has to be worth the penalty in performance.
IMHO, if you're at all concerned about your 300C's performance, look for a nice 20" single-piece, forged wheel. They'll actually weigh less than the stock setup, give you a more sporting look and unlike the high-end, forged modular approach, won't cost you 25% of your car's purchase price
Of course, if you're more of a cruiser and less of an adrenaline junky, there are plenty of nice (albeit HEAVY) cast aluminum 22s out there to roll.