I agree with <b>endyen</b>, Socket754 will become the "low-end" platform. But I don't think S754 is a bad choice, this platform can be upgraded up to 3700+ and S939 is not actually ready for PCI-EXPRESS. So both 754 and 939 have a limited lifespan in terms of GPU upgrade. But, There is tons of AGP based MB that are sold averyday, so we will surely see AGP cards for a long time in the store shelves. Think about it, we still see PCI Video Cards for sale (low-end only).
Personnaly, I plan to upgrade too in late august/september and I will buy a Chaintech VNF3-250 (S754) with an A64 2800+ or 3000+ aven if PCI-EXPRESS is not available, because i know that X800/6800 based Video Cards will be around for a while and they are damn good performer.
My main concern is to get an X800 or a 6800GT??? I wait to which GPU will offer the best price/performance in 2 months!
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It's tricky to use words like <b><font color=green>AMD</font color=green></b> or <b><font color=blue>Intel</font color=blue></b> in a signature some users could think your are biased.