If you are going to spend the money on a 2pc rotor setup you should do one that is full floating if you really want it to work as advertised.
or this style
I perfer the top style because there is less chance of a hat failure IMHO.
Also, the bolts on the top one should be safety wired.
2pc rotors like others posted in this thread that are simply bolted to a aluminum hub don't offer nearly as many benefits and are prone to failure when tracked hard. They do not allow for expansion at the hub joint and as a result can cause fractures at the hub resulting in failure. They also do not help at all in preventing knock-back on the pads that all sports cars see as a result of hub-flex. This is even more true if you are a hard driver and really push the curbs as they cause a great deal of deflection.
A pretty cool video showing some deflection from curbs on F1 cars. (No one takes these kinds of footage from normal race cars! To bad cause its pretty sweet!)
http://www.streetfire.net/video/f1-in-slomo_695288.htm
-Your Pal
Fishey