A GeForce 6600-6800 Ultra will run lost coast on high no problem. if they can run Splinter Cell Chaos Theory maxed no problem because SCCT has pretty much the same features as lost coast.
for SCCT:
HDR Lighting. check.
Parallax mapping, check.
Soft, dynamic lighting, check.
all of those isted above together will only work if a card has Shader Model 3.0, do ATI cards have that, no. ATI cards are stuck running it in the Dx 8.1 SM 1.1 paths. so essentially, Splinter Cell Chaos Theory looks EXACTLY the same on a GeForce 3 as a Radeon X850XT-PE.