PCIe above version 2.1 may create compatibility problems with PCIe version 1.0.
7750/7770 cards are PCIe of version 3.0. Therefore, before you buy one of them, please ask the retailer about your concerns on compatibility and returning the card if there is a problem.
You should also check if there is a BIOS or firmware update on M/B manufacturer's web site that may bring a solution to compatibility issues.