Took me a while to figure out but I finally got my GT720 working with full acceleration in yosemite. I booted with the nv_disable=1 flag to get past that loading screen. I guess it depends on your system
I may have done some extra things but I installed the latest nvidia web driver and then I had to do a few extra things. I used chameleon wizard to drop a MacPro2,1 smbios, I disabled all the ATI, AMD and intel drivers. Then I also added nvda_enable=1 and graphicsenabler=1 to my chameleon configuration.
Also: unless I misunderstood you, please don't insert a pci-e card after you booted your pc every again