Riva stage 1 kit that you have installed (gave) you about 4-5mph more than stock at a cost in the neighborhood of $700
Now the fun starts as hp/mph "really" gets pricey..
Stage 2 with an upgraded SC rotor + blowoff etc will give another 4-5mph (over & above stage 1) but now the jump will be 5 times the 1st stage cost! 3-grandola and up. Stage 3? hehe, better rob a bank and almost double the stage 2 price. -Since- you already own half the parts in stage 2 (in your already installed stage
The chip referenced must be an ecu chip which enhances fueling/timing, minor with gas engines compared to diesel where the chips then pay BIG dividends for just a few hundred spent. Most feel ecu chips in pwc's are to be for the "bored out of their minds" type of people
Bottom line.
Stage 1 by Riva is a great deal for the bucks vs. the mph/gain game. Anything more is for the heavier pocketbook folks.