If your budget permits, I recommend you to look close to the top of charts to get the maximum performance in Mocap Studio. Like GTX 970, GTX 1060 and above.
vmaslov wrote:
Modern gaming cards can be installed in older desktops having PCIe x16 slot (and one empty slot nearby, because gaming cards usually occupy place of two slots) and power supply unit with sufficient watts (look for required minimum in videocard specs).
A couple of other things to note.
It may be required to update the BIOS of your motherboard to the latest version. For instance, my older PC (based on Intel 7x series chipset) did not boot properly after I installed GTX 970 to it until I had updated the BIOS.
Modern videocards usually require additional power connectors (6/8 pin) from PSU. So make sure your PSU has appropriate connectors or other available connectors (e.g. Molex) which can be used with 6/8 pin adapters.