It's the same 4 piston style caliper, just the ears are longer to accomodate a 345 rotor instead of a 330 (we've been talking about different supets on MBWorld)

I personally did a rear brake upgrade on my C55 to an older CL55 that uses a larger caliper and 315 rotor, which leaves me with the removed 300 rear setup that's also found on the SRT. Looks like I might have me a free SRT rear brake upgrade once I get my car....