There is a GREAT difference in using SIngle and Double in 64Bit compiler in XE2. Double in XE2 is faster twice as Double in XE and below. BUT Single is 3 times slower than in 32bit. And 5 times slower than Double.
So, use Double whenever it's possible.

Didn't notice link given by Lifepower about this new "feature".
Embarcadero still advice to use Double instead of Single.