Achilles, if you're looking for a ridiculously cheap solution that would cost you less than half of what a GTS 250 would, then look no further than this card
. This is the older (and better) 96-shader model (the new 9600GSO only has 48 and isn't worth buying). It might not have 1GB, but 768MB isn't too shabby at all and is probably all that the card can handle. When overclocked, this baby is roughly comparable with Astro's 8800GTS 640MB. The only hangup is the cut-down memory bus, but I have one of these cards myself and both the core and the memory overclock very well. I've got mine at 650/1630/950 (core/shader/memory) and I haven't even begun to push it yet.
Best of all for your case, this card is truly single-slot and will not intrude into the adjacent expansion slot on your motherboard. Even so, its cooler is still effective because it has a shroud that directs airflow over the memory as well as the GPU. This card is easily twice the card of your 8600GTS. You can't do better for $50.00, and this is the most sensible upgrade for a computer that's approaching 3 years old, IMO.
The rebate is large, yes, but PNY rebates are known to be reliable. As long as you jump through all of the hoops you'll get your money. I bought one of these for the workstation that I'm borrowing from my folks, and right now it's making a lot of sense to get a second one for the computer that I'm building for a $100.00 SLI setup that would approach a GTX 280 in performance. I just need to find a good, cheap SLI motherboard and decide whether to go with an Intel or AMD CPU.
"They should rename the team to the Washington Government Sucks. Put Obama on the helmet. Line the entire walls of the stadium with the actual text of the ACA.
Fix their home team score on the board to the debt clock, they can win every game 17,000,000,000,000 to 24. Losing team gets taxed by the IRS 100%, then droned."