So more power on paper but less torque for the XKR-S. You might think power to weight would be in its favor with its convertible soft top versus the hard top on the SL but at 4,079 pounds it barely undercuts the 4106 pound SL63 AMG. Torque to weight is certainly in the AMG's favor and if these cars hit a dyno power to weight likely would be in the SL's favor also.
The SL is the first to hit the track and does a 1:23.9 laptime. It is more of a GT than a sports car but it shows minimal body roll. The XKR-S is said to feel lighter with its steering but that it has more body roll. It also struggles to put its power down essentially constantly wanting to be sideways. That certainly is a fun personality compared to the SL63's business like demeanor but it does not result in a quicker lap. The Jaguar does a much slower 1:25.7.
The Jaguar certainly appears to have the more entertaining personality of the two but it also looks to be a bit of a handful that struggles on the track. Is that more fun? Well, that depends on your personality.