10.10.3 only boots with 6970M disabled via command line - otherwise Grey screen

iMac (27-inch, Mid 2011)

3.1 i5 w/ 12GB RAM

AMD Radeon HD 6970M 1024 MB video card

Upgraded to 10.10.3 was a happy camper. It boots up, yay. Then about 15 minutes later in Safari the screen flashes like mad and goes dark. I reboot and now am greeted with a 1/2 way loading Apple front screen and then it will reboot itself. In a loop.

If I try safe mode it loads 1/2 way then goes grey screen and sits there forever. I've tried it all, if there is a key combo to press at boot I've been there done that today lol.

Found a link on the web explaining how to disable the video card and use the onboard integrated graphics. Moving the Extensions for ATI* and AMD* to a temp folder. Restarting and.... HUZZAH!! Now I can get into the computer but as you can imagine it's not ideal and everything is at a CRAWWWL. Running programs I need for work like InDesign is just a miserable experience right now and work just can't get done like this.

Anyone else in this hot pile of doo doo with me? I'm down with being the guinea pig of ideas for the greater good of mackind but tonight I'm probably going to just back everything up and format this thing clean. Unfortunately if it's a Yosemite Software issue (which from all the similar posts inhere I'm guessing it is) it probably won't help me other than keeping me from smashing my head against the wall.