Unofficially difference between Corsa's and Hero's on Gallardo SL on long twisty track like Nordschleife is only around 1s.... New Hero's are much better then any tire on dry track and they are pretty decent on wet road as well.

Interesting enough Sport Auto wet handling champions are Porsche 997 GT3/GT3RS(Michelin Cup's N0), 997CS(Michelin Pilot Sport 2N1) and Audi RS4(Pirelli Corsa). New R8(Pirelli Corsa) was also pretty good. All were much faster on wet handling track then 599, Z06, 997 Turbo or Gallardo SL for example.

Back to your question-I expect CL63 to be faster on wet road then 599. CL63 features pretty agressive ESP setup and Conti's are much more wet road friendly then Hero's on 599... 599 is a awsome car but, it is not all weather interceptor...