NVIDIA GeForce 9500 GT 1gb isnt bad at all.. but i have an GeForce GTX 950 sc+ acx 2.0 with 2 gbs on the way as an upgrade .. only upgrading for the 4k video support and direct x11 features so that i can play fable legends (the gpu happens to have direct x12 ) .. from my understanding any pci card should work ... i will admit a new motherboard would be a great idea .. but the gpu will work on the new motherboard down the line once you get there .. i also have a Intel Xeon E5450 on that mb, its not ment to fit but i cut a few tabs off the slot and it works great! (google about that more before you try it yourself) my pc is really zipping along for having a 8 year old motherboard , my "chrispc windows index" is 7.4 for cpu and ram.. 5.1 desktop graphics and 9.9 gaming on a scale from 0 to 9.9
The PCIe interface is backwards compatible, and you could use a higher or lower gen PCIe card in your system. However, it may limit the performance of the card if it is a higher PCIe gen that in your board (PCIe 2.0).
I would like to recommend you to visit the following article where you can find some more information regarding the differences between PCIe generations:
From the article: "The potential for increased data throughput and performance within any computing platform is the primary difference between the PCI Express 3.0, 2.0 and 1.1 interfaces. A PCI Express 2.0 board installed in an industrial computer will send its data to the system host board twice as fast as older PCI Express 1.1 boards."