New
#21
Now it may not be relevant to your situation with your old Intel board, but a few years ago I had an incompatibility issue with several older boards and a more modern graphics card. I was forced to make some hardware adjustments (i.e. putting the graphics card in a second machine instead, which didn't exhibit the problem).
I had a Supermicro C2SBX board, which had two PCIe 2.0 x16 slots. I was trying to install an HD5770 card, which purports to be PCIe 2.1. Well, when the HD5770 was installed the machine would not boot. Instead I got the 1-long, 3-short "beep code" error, which indicates a graphics issue. I simply could not use that card in that machine.
However I could install the same HD5770 card in an ASUS P5Q3 board machine, which also has two PCIe 2.0 x16 slots. And yet for some reason, the HD5770 was usable without a problem in the P5Q3 but not in the C2SBX. I had to stick with an older HD4850 card in the C2SBX machine.
Eventually the C2SBX board died and I upgraded that machine with a new ASUS P8Z77-V Pro board, putting the HD5770 in it. I shuffled hardware and put the HD4850 into the old P5Q3 machine. So far everything works fine.
Well I later decided to upgrade the HD5770 to an HD5870, and tried to move the HD5770 over to the P5Q3 machine (where it had once worked just fine) to replace the HD4850. It didn't work properly. Yes, it still booted, but its onscreen performance was very odd with lots of "flickering" of images. I tried assorted Catalyst driver versions thinking they might be responsible, but nothing helped. I finally had to go back to the old reliable (and WONDERFUL performance) HD4850 card in the P5Q3 machine, in order to get video back to normal.
So, although in theory it might be possible to use newer graphics cards in older PCIe 2.0 boards, I'd be at least a little conservative in my optimism before actually trying it out. YMMV.
On the other hand, I've never had any performance or compatibility problem at all using older somewhat slower low-power cards (e.g. HD5450, HD5570, HD6450, HD7750) in both older and newer machines.
Again, YMMV.