Rallisport challenge is heavily dependant on sound card if you use doppler effect. And there is a known bug with the lens flare option.
With lens flare turned off and all options on highest except for opponent car sounds, doppler effect, and weather, I am getting average fps of 50 and highs of 95.
You're doing something wrong in settings. If you need a walkthough then I can give you some pointers.
You're either a fool or an idiot for posting your 9800 at 1550, I don't know which but if you're a fool it's better to keep your trap shut and not be validated than open it and remove all doubt.