I think I read somewhere that the human eye can only see at 59 fps anyways, anything over that you're not noticing any visible benefit.

However, lag spikes due to machine lag DO happen and the higher your average framerate the more of a cushion you have to reduce the impact of the lag spike.

I personally hate it when I log into a single toon only in Dalaran and I can't even move (frozen on the spot) for 30 seconds while it loads all the textures and graphics and the hard drive thrashes away. At least in TBC and Vanilla, it would take forever to load graphics but you could MOVE while it was loading. For some reason in WotLK they decided to make it so you cannot move while your machine fetches things.

Yep, remembering the old days of logging into an Ironforge that was nothing but shadows moving on the ground for the first couple minutes...but at least I could steer my shadow around! My buddy was worse off, he had to zoom in to first person and point his camera at the ground at his feet, navigating only via the minimap, if he wanted any hope of being able to not lag out to 0fps in front of the IF auction house...