To simplify horribly, when it comes to video cards right now there is no real line between "I'm a hardcore gamer" and "I'm a casual gamer" in getting the next generation (and some current gen) titles running well. This is a direct result of the fact Consoles are winning the war (i.e. most games right now essentially can get away with an "XBox 360" being your minimum hardware requirement, which for some reason is turning ported engines into monsters) and the fact the latest gen engines which are specifically targeted towards PCs seem to have completely overshot the hardware out there now.
Further complicating this is we're just at the very beginning of a trend to exploit GPUs for what they really are -- massively parallel processing engines -- which has implications far past gaming. Hardware accelerated decoding is just the beginning.
All in all though, if you want to do any gaming at all, I would really forget about the 8600GT and expand your budget $65 or so to get a HD3850. It's the best price/performance ratio out there right now, and hopefully keep you happy.
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