my CA went to Cali a couple months ago to drive the M3 and a lot of its "competitors" as part of a training program. cars included the c63, wrx sti, and the is-f. i expected him to talk mostly about the c63, but instead he said that the is-f was a "great car that grossly exceeded his expectations". here's a guy that rarely praises non-BMW cars, but apparently his team is focusing on the is-f as the M's prime competitor, not the c63 which surprised me. of course, every dealership will be different. he said the c63 was "pretty nice" but quickly gave the nod to the new M3.
for the record, he called the wrx sti a "piece of junk" and was insulted that the training class included it as a "competitor". haha.