I have a CLS55 and all i can say its amazing on take off, it feel much quicker then the ISF, but the ISF top end is amazing especially when it opens up after 3500rpm, so both are probably equal 0-60. The sound on the AMG is far better then the ISF, i said that even when i had the ISF.
I was looking at Jags too.. but just didnt seem as attractive as ISF or the CLS.
Drive wise the merc is effortless, spend £1200 on a remap, 84mm SC pulley change, x pipe, 2nd cat n res delete your looking at 550bhp with over 600torque. Thats a super car killer (tested). I love the AMG.
But guess what.. there is just something about the ISF one cant expalin. And thats why i want another.