From my limited research on the net, the Saleen S281 SC has 350 HP and the Stage III Roush has 390 HP. They both have suspension upgrades and body kits and stuff. I'm not sure which one is better though. I like the look of the Saleen, but I also think that the Roush would probably be rarer and it has some more jam (40 HP).
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White 1995 Mustang GT
Dynomax Cat-Back, Offroad H-pipe, K&N Filters w/o Air Silencer
My 1995 Mustang GT