The 550 Ti isn't a PCIe 3.0 card anyway. The 600 series from Nvidia and 7000 series from AMD are the only ones that are at the moment. But to answer your question completely, no, not having PCIe 3.0 capability isn't a problem with a 550 Ti.
Also, no extra performance with a PCIe 2.0 card on PCIe 3.0, just to clear that up.
Ahh, well with it saying PCI-Express i assumed it was 3.0, but that has cleared things up! Thanks a lot