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@swatski did a ton of testing with Impellers on his SX190. Basically found that the stock 6CW was the best all around solution. His testing threads are around here somewhere.
Have you sealed the intake tunnel and put an L13 cone on yet? Those are both far less expensive and will all but eliminate cavitation. Also, I'm unsure what boating experience you have before the jet, but you have to adjust your driving style to the jet propulsion. Hammer down while turning won't work. Ease through the turn, then hammer down once pointed straight.
The L13 or WetWolf Cones will definitely make an improvement. People who say otherwise were most likely hoping it was going to solve cavitation caused by other issues.
Call Glen at Impros and have him either re pitch your impellers for high altitude or buy an additional set and have him pitch them for high altitude. There are a lot of very satisfied customers that Glen has set up high altitude impellers for.
If you are after improved low end performance and Glen at Impros suggested the dual impeller set up you can be sure that you will get increased low end performance without cavitation. If it was me, I’d have my oem impeller repaired and keep it as a spare In addition to the new dual impeller, and replace the wear ring.