You will not find the gtx750ri in PCIe 2.0 only form. PCIe in theory is forwards and backwards compatible for now.
The 750 you noted is a GO TO card for many systems. Most don't need a new PSU and it's a good bump for the money.
I am upgrading my video card and all the cards I am looking at are pci-e 3.0 but my 3 year old machine only supports pci-e 2.0. Should I change my requirements for a new card to only 2.0 cards? Will I be wasting money buying a 3.0 card? I am looking at spending approx $100 and I like the gtx 750ti but is it worth the $ with my 2.0 machine? I currently have a GT 530.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic