The eVGA SuperClock is way, way faster than a 7800GTX, so it's way, way faster than a 7800GT. Here's what MunkyMark06 says about F.E.A.R. performance when set at max, 4x AA/16xAF, no soft shadows.
7800GT 400/1000: 32 FPS
eVGA 7800GT 450/1100: 35 FPS
7900GT 450/1320: 42 FPS
eVGA CO SuperClock 7900GT 550/1580: 51 FPS
Be advised, however, that the SuperClock is currently Out of Stock on eVGA's website.