So I have quite an old computer, it is a prebuilt Gateway LX6810-01, it has an Intel Core 2 Quad Q8200 CPU, 8 GBs of DDR2 800 ram, and an NVIDIA GT120 graphics card. I also have a 600 watt PSU. I was wondering if my computer would get better performance in gaming by adding a GTX 750 Ti graphics card, or if it would only give me a marginal fps boost because of the older CPU, RAM, and motherboard. Also, does PCIE 2.0 decrease the performance of a PCIE 3.0 card? I plan on upgrading the other components sometime later this year or early next year. Thanks in advance.
your better off saving your money and buying all the parts at once. both amd and nvidia are going to be dropping newer cards latter this year and next year. nvidia maxwell is held up do to yield issues on 20mm parts. last nvidia demo show they already showed off the replacement gpu for maxwell. the end of this year is when intel dropping the replacment for haswell cpu.
The GTX 750 Ti would be a perfect upgrade to your system. It doesn't require any additional power from your PSU (it gets all of it's power from the PCI-e slot = 75 watts max).
You should see quite a bit of FPS upgrade going from the GT 120 to the GTX 750 Ti!
The PCIe 2.0 downgraded slot from the PCIe 3.0 GPU shouldn't matter in your case. I think the dual GPU's R9 295x and Nvidia's GTX 790 are the only GPU's that would see some decreased FPS from a PCI-e 2.0, IIRC (read it recently somewhere).