UGH! It really is a personal thing... some people do better in heat and some in cold (oddly enough this was a topic during the Tour coverage last night too!)...

I'm a cool weather rider... when it's too hot I just cannot ride the distances or the speeds I can when it's cool out... I seem to overheat no matter how much I drink... especially if there's any climbing whatsoever involved! And I DO ride in dry heat... SoCal... doesn't get much drier!

If you typically do well in above 90 degree weather, then most likely you'll be fine... I, however, would be at home under a biiiiig fan!