I also have the thunder shift kit on my '01 SRX700. I was hoping to find where yours ended up, but I don't see any results posted here.
I keep adding weight to mine but I'm getting no where fast. I have 38.4 gram base weights and after upping the screw weights for the fourth time, I'm still seeing next to no change in shift RPM. I just put in the following: hole 1; 5.8 grams, hole 2; 4.2 grams, hole 3; 3.0 grams for a total of 51.4 grams per weight. Engaging at 4200 and shifting at 8800, but that's exactly where it was shifting before I just upped each weight 1.9 grams (1.2 added to hole 2 and .7 added to hole 3).
Those with experience in this area, how much more weight would you throw on to get the shift RPM down another 200 to 300 RPMs?