How much of a bottleneck?

How much of a bottleneck would it be to have a stock E8400 and a 580GTX?

Your system will definitely bottelneck that video card... You would need a pretty fast system to use that card at its full potential. You will still see a difference in graphics performance over your current card but your next upgrade would have to be mainboard, cpu and RAM going to something like an i7 set up which = $$$

A lot more than my Q9550 bottlenecks a GTX 470.

You´ll need an AMD x6 or i7 9xx for that GPU.

Once I get some new cards I'm gonna do some testing on old setups running newer cards I've got a 7900 GT 256mb, a GTS 250 512mb, and soon to be an HD 5670 lo profile, and a GTX 460. I can run these in my signature system and in a Dell Vostro 420 with a Core2Duo (maybe not the 460 or the 250, gotta check the power supply dongles in the Dell) and see what kind of numbers we get from 3dmark05 and 06 (XP on both these machines).

I can also run numbers with the cpu at different numbers, like 1600, 1800, 2000, 2200, 2400, 2520 (as fast as this Opteron will go on stock heatsink ) with each different card and see what kind of scaling we get...I don't have a newer system than these two, but I for one am interested in seeing what we get. I'm thinking max of 16,000 marks in 3dMark06 from a GTX 460 1GB with the CPU at 2520. These do 20,000 with an i7 at like 4.3 ghz right? I get 9334 with the signature setup in 3dmark06.

Anyone else interested in seeing some old school hardware bottleneck some old and new cards?

Don't hook up a high end card to a crappy dell powersupply... sizzle sizzle

Of course It probably doesn't even have PCI-E power dongles anyway. I got the OCZ 520, assuming it has all the Mobo connectors needed for the Intel setup, that could power everything fine.