No ownership with IS-F, drove friends' few times and I guess they are good for fun dd, but that's it. you can't do much performance wise.
I've owned both E55, C63 in the past(just sold my C63)
Between two, I liked C63 more. Although you can do more stuff with 55 engine, because of its platform of being a larger sedan, It just felt like driving a boat.
But with C63 it feels more like drving a sports car than a sedan. Tighter, rigid, and 'imo' more reliable. Gas mileage with both cars though.... sadface
I had mine tuned by Techtec germany and it was perfect for dd + fun highspeed runs on the weekends
how about M3(E90) sedan?
Not as fast as AMGs on a straight line, but fast enough to enjoy daily wise, good looking, fun for curve-oriented driving