would putting another 256mb 8600GTS in be worth the $120? please help

so as some of you know ive been working on upgrading my crap DELL into a gaming rig and it went pretty well
but the crap mobo that dell gives you is pretty much bottle necking my proformance
so i did some research and dell sells motherboards to fit there machines and i could get an SLI ready one for not to bad of a price and I would be happy for a while but at some point if i put another 8600GTS in there what kind of proformance would i get?
i have 3gb DDR2 ram
Intel core 2 duo at 2.8GHz
Vista 32bit
and 256mb 8600GTS

no? nobody can help me

well i guess a better question is, is it worth the extra $120 for another 8600gts? will i get a a big enough boost in proformance to be worth $120?

hmm... I would say go for it... but, if I were you I would save up another 150bucks and get you a 8800gts (g92) wich is going to outperform 2 8600s anyways.Shrinekeeper

well thats my plan, im a college student so i dont make much money right now
but over the summer ill be working full time and making good money so im just trying to get something together for about $500. ive spent 280 so far and a new mobo plus another card will cost me about $250