No first hand experience with trying different impellers on a stock ski.
general consensus (from my reading) is to stick with the stock replacement unless you plan on adding other mods.
I've also read that solas 15/20 and 15/22 are a good choice, but most of the speed junkie posts i've read indicate that if its all stock/ stay with stock prop (14/24?)
I'm running 15/22R in my 08 and I've been happy with it, but I'm running riva stage1. I can certainly tell the difference.