Ignoring the fact that $100 for a 5500-class video card is an absolute rip-off, why would pay more for a similar card that you're not even sure can OC to your 5500's levels?
Anyway, used 9600Ps should be close to $80 and will smoke any 5500.
To the OP, CyberZenn is right. What's your price range, though? Yeah, 9600s are out of the cards for you b/c they require an AGP 4x/8x slot, but can you find a used 9500P for about as much as a new 5700LE? If so, grab it, as it'll be about as fast as a 9600XT. I don't think the 9500P requires a 300W PSU, but you'll probably want at least a *quality* 235W one.