That is probably PCIe 1.1 A lot of p35/g33/g31 have 1.1 into it. Pure 1.0 PCIe lasted quite short before changed with 1.1. Anyway if the GT610 works, then the 7750 will work. Don't worry.
For your purposes, it doesn't matter which revision it is. The different PCIe revisions are forward and backward compatible.
You can find out by checking the motherboards product page.
Assuming the system was built/bought after ~2007, it should be PCIe Gen2. If it was bought very recently, then its likely Gen3.
That is probably PCIe 1.1 A lot of p35/g33/g31 have 1.1 into it. Pure 1.0 PCIe lasted quite short before changed with 1.1. Anyway if the GT610 works, then the 7750 will work. Don't worry.