Skat 9/17 props work great on a sxi. You could use a standard or c75 mag prop
I did a lot of research on this topic about 6 months ago. This ^ is what I consistently came up with. Many people recommended to go with the Skat 9/17 C75 impeller. It has a larger diameter hub on the impeller. Even if you don't run a different pump (which the impeller is intended for), the larger hubbed impeller with the C75 series is apparently great with the stock pump. Something else many people recommended, is an 80mm nozzle (which your boat might already have if it's an SXi, and not the SXi pro). Or you can try running the reduction nozzle from a 650sx which is apparently larger
Other options I came up with are:
Solas Concord 11/16... but have it repitched to 9/14
OR
Skat Trak 8/16... I assume with this would be good with a stock diameter SXI Pro pump which is somewhere around 76mm I think.
Most people recommended the C-75 9/17 by Skat Trak