First off, I think your choice is kinda skewed since you are comparing 2 tryes from different classes.
The Michelin Pilot Road 2 is a tyre that sits in the Sport Touring category and was created to cater to riders who primarily do lotsa road mile, like touring and commuting. Its emphasis is on wet weather grip and durability.
The Pirelli Diablo Corsa 3 is a tyre that was designed for fast road riding, with an emphasis on dry grip and fast warm up times. The Pirelli Diablo (without the Corsa) is a road focused tyre. The "Corsa" word means "race", Geddit?
You should think about comparing the Michelin Pilot Road 2 with Pirelli's Diablo Strada, which are in the same category, or Metztelers Roadtec Z6.
On the other hand, Pirelli's Diablo Corsa 3 should be compared with Michelin's Pilot Power 2CT or Metzeler's Sport Tec M3.
On a personal note, I have a few friends that have run Michelins Powers in the past. They both love the tyre so much that they have become repeat buyers. One of them even did 5 or 6 trackdays on his 180 bhp K5, and sold it to another friend who used it for commuting and a trip to Cameron. Overall, its excellent.