factory tuning limited only , the 05 SL55 was 493 the engine from the 07 sl55 was 510hp this had the larger throttle body and a few other upgrades to the engine which was also in the g55 till 2011 I think.. Honestly all the e55 felt the quickest, I have driven a bunch compared to the heavy A$$ SL.. So its just tuning, engines are the same. Here is a good wiki read.
The E55 AMG is powered by the m113 engine, a 5.4 L v8 with a Lysholmtype supercharger manufactured by IHI. The E55's engine was tuned to 476 PS (350 kW; 469 hp) and 700 N·m (520 lb·ft), the low end of the supercharger 55 range due to its longer exhaust system, compared to the SL55 engine at the high end which made 517 PS (380 kW; 510 hp) and 720 N·m (530 lb·ft). Despite this, Car and Driver reported in their testing that the E55 AMG was faster than the SL55 AMG. The E55 AMG was the fastest four door car in Mercedes-Benz's lineup at the time, being quicker than the C32 AMG and S55 AMG, and it posts faster acceleration than the 2003 Brabus E v12 biturbo (verified by the Guinness Book of Records as the fastest saloon of the time)