As far as I heard, both the SL 55 and CL 55 have practically the same performance, the SL 55 may be being slightly faster from 0-300 kph. We didn't do any SL 55 vs. CL 55 comparison, so this is pure theory now.
The only thing we know is that the E 55 slightly outruns the SL 55 from 0-300 kph, difference shouldn't be very noticeable though.