The GT has GPU clocked at 560Mhz (rather than 420 on GS) and memory clocked at 1300Mhz (vs 400Mhz).
Either card will be a HUGE difference over an FX5200
Check out this
chart on Toms Hardware the FX5200 is down the bottom. Now compare the top card on that last 6800Ultra with the 7600GT on
here.