I had a 335d new back in 2007. I had it remapped by Evolve to 365bhp and 570lb/ft, it did 13.2-13.3 sec 1/4 miles at Santa Pod and 167mph at VMax. It featured in BMW Car Mag in a shootout with standard and tuned 335d & 335i's. It was on a par with an E90/92 M3 (414bhp) from s standing start to 160mph. On the move it would always have the edge but would never pull a big gap. At Santa Pod the M3's were doing similar 1/4's if launched well, the M5's (500bhp) were doing 12.5-12.7 sec 1/4's. On the move an M5 would struggle to drop the 335d.
I would expect a remapped C63 to be quicker than the 335d, not by that much but enough to be able to reel it in.
Jules.
my C55 does the 1/4 in the same time. A Stock C63 is high 12's.