Member?.....
There is a member who has modded his RXP with the RIVA stage III. He's pretty good with the 4-TEC mods. You might want to look him up and drop him a PM, see what he has to say. His name is "meirvin".
In my opinion, the cost of what your looking to do, outweigh the benefit of added speed. You can go with a new intake grate, helps you hook up faster.
There just isn't a whole lot you can do with the 4-TEC without major kit changes outside of impeller and grate. Maybe a new power nozzle.
Check with meirvin, see what he has to say.:cheers: