Corsair H100 vs V8 Watercooling Kit 240

[MNA24]

What sort of performance difference would you get when comparing a Corsair H100 and a V8 Watercooling Kit 240 from OCUK?

Is it a great leap in cooling performance?

 

[MNA24]

hmmmmm......

I have another question, would a 240mm + 120mm rad have enough cooling capacity for an overclocked CPU and SLI stock GTX 580s?

 

[MNA24]

Corsair 650D, ive seen 200mm rads on the front intake but it involves a dremel to trim the drive cages and its not something i'd be comfortable with when moving to water cooling for the first time, just want to keep it simple.