GTX 750/GTX 750 Ti have long been a recommendation in this type of situation, in order to avoid crossing over that BIOS/UEFI threshold. And even if that wasn't an issue, given the CPUs, you probably would see limited benefits above a GTX 750 Ti in most cases.
Now, the PSU question is the key one. The 750 Ti, when it's not an overclocked model that requires supplementary power, can run on a lot of mediocre PSUs of the time. But whether these old PSUs are good, mediocre, or scary junk is something that has to be cleared up before any purchases are made. I will never recommend any GPU until knowing this information.