They're the same internally so you'll have similar temps. XD is a little more enclosed so will be slightly hotter. After a lot of intense gaming, maybe an 30-45 minutes you'll find the center of the XD is hot, but not enough where it would be uncomfortable.
High temps can lead to CPU throttling and then decreased performance but I've never really experienced it. I tend to play in short bursts though. The longest I play is maybe an hour in the game Xenowerks which is fairly graphics intensive and it runs silky smooth.