I just downloaded the Eclipse 4.3 integration build and I’m stunned by its performance improvements. You find the currently download for the Eclipse 4.3M3 build under the following link: Eclipse downloads. I selected I20121113-0800.
I measured the performance improvements and here are the results visualized as a nice graphic.
I should probably add that I made the above numbers completely up.
But the integration build feels much faster to me. I think the main change was done in Bug 391868. Also Mylyn seems to have solved there performance issues in Bug report in their latest build, so for me the Eclipse IDE is lightening fast again.
I suggest you download the latest build and test it. Please report additional performance problems in the platform via Eclipse platform bug, if possible with a pre-analysis of the performance problem.