Yeah it doesnt take much to make MySQL much quicker.
IPB still needs some work. For eg, when you go to page 2 of a 100 page topic, it will select ALL posts then find the posts for that topic and THEN order them and THEN display the ones for page 2... hence why, at this stage, the whoretown threads kill the system.
IPB 2.3 is being released soon with heaps of performance upgrades... should be much better.