Well, it's simple laws of physics regarding the rotation speed. a faster rotation speed for a mechanical hard drive means lower seek times, but it working faster means it's generating more heat.
Your biggest problem regarding a hard drive in the ps3 is the interface limitation. It's a big reason why putting an SSD in a ps3 doesn't do jack for load times, and in some cases even makes it worse. the bottleneck is in the ps3 itself in handling it, so there's no sense in putting a faster hard drive than necessary in the console.
That being said, if you can afford to get a model with a larger buffer cache, do so. That at least would overcome the time it would take loading or writing data to the disc.