Yar I be havin an 8800 Ultra and my frames be sailing smooth in Pearl.
Hoist the flag and take a peek in Nvidia Control panel and ensure you allow negative LOD (do not use clamping) and make sure Multithreading is turned to AUTO.
You may wish to tweak other settings.
Argh, I know that the GTS isn't as great as the Ultra but you should be havin no problems with it in SH4.
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