I don’t have RXTX’s but GTI’s… But assuming identical skis and conditions (water, fuel octane, engine/supercharger performance, wear ring condition, and driver weights identical, etc.) an additional rider of average weight (150-200 lbs) does impact GTI top speed about 3 MPH in my experience. I would think even with RXTX power capability, there would be some impact with additional weight in a similar way. Those that have twin RXTXs may have a real world test example…