If you have a 100% stock boat then invest in a pipe first. For me the addition of the pump was/is most noticed in staying hooked up in certain conditions. white wash, hard cornering and light chop . So think - surf riding (I don't do that but I assume) with waves crashing and water being aerated.... Racing your buddies and crossing through their jet-wash, etc.
I wouldn't say the pump makes the boat faster per se - but because it is more efficient in keeping your pump loaded, in some conditions you will be faster. Make sense?
glass water drag race - ski with pump and ski without pump - I'm not sure one would edge the other by anything major.
In fact my buds just raced like this - same skis - Bpipe & MSD - one with stock pump one with solas mag and 10/16 hooker and they were dead nuts even