I agree with MattyG, the SRX sounds to be "Maintained" rather than "Modded". A lot of guys have long traveled their SRX's on this site, many have sent in powervalves to Yamahead to get the SS Bolt mod, who wants to deal with a pull-thru mid-season? I go through the bearings on my sleds at 4k-5k miles, re-rung/new piston my Viper at 5k miles. It might have been early, but my SRX had 6000 miles on a set of rings and one decided to let go, took the piston and cylinder out with it. That can end a season real early.
I'd buy em both, lol... I had a 98 SRX and have an 02 Viper, I wouldnt buy another 98-99 SRX, I hate the headlight, but a 00-02 had the good headlight, which are almost as good as the Viper headlights. The seats on the SRX's are good, but the 04 Vipers are better (IMO). Comparing those things you are just cutting hairs between em, the real question is do you want 120hp or 140hp?
I opted for 120, because I like the looks of the Viper, and it made a great sleeper, im still waiting to line up with an 01 SRX just to surprise em a bit