Anyone feel like their car gets way too much body roll? I know I can get springs to help but it would ruin the already terrible ride quality. An M4 seems like a more feasible option for a next car if the 63s is similar to the 43 in terms of handling...

The C63 is a completely different driving experience from the C43. The former is RWD whereas the latter is AWD. You're going to get less understeer tendency, more oversteer tendency, and less body roll with the C63. That's just the way it is. The AWD car is going to ride higher, and is less apt to rotate (thus creating the sensation that it is more prone to roll).

That said, compared to most AWD cars, I find the the C43 is actually pretty capable from a handling perspective. It doesn't understeer like a pig, it grips, and it's incredibly predictable.

At the end of the day, its maximum potential is just shy of the C63. C43 tested at 0.92 g on a C&D roadholding test, whereas the C63 achieved 1.02 g. The difference between the 2 is, most people aren't going to be able to safely extract that potential out of the C63 on the street.

In addition to all that, a large chunk of the handling performance is going to be determined by: a) which wheel size you're running; b) which tires you're running (and the pressure); and c) which suspension mode you're running.

I think the handling is great. The biggest thing you can do is get rid of the runflat tires. Got high performance or all season high performance and the grip will be greatly adavanced. Lowering springs might help. But I’ve had hr springs on other cars and ride quality was terrible. If eibach makes springs I would go with them.