Revisit graphics card upgrade/replacement for Early 2008 Maa Pro

I have read posts back into 2012 on this subject because the rubber has hit the road for me-I want to run three or perhaps four monitors (Samsung Synchromasters-22") on my beloved Mac Pro. MY Radeon 2660 is still running ok, but, of course won' support more than two displays. Based on another thread here, I'm planning on getting a GTX 650 and running both cards. I run Mountain Lion because I use the "spaces" capability of that system which appears to not be available in Yosemite. I am not a gamer, but use a streaming trading system that likes to have multiple monitors.

I'm a retired techie, but have just had a need to use a tech service to recover some files that I lost in a re-setup of boot camp on one disk. He has counseled me to not use the GTX 650, saying it will not run reliably on my system and that my monitors may not work. At this, my tech background takes that as a challenge and I have a source for the GTX card that allows for a 30 day return. Nevertheless, I thought I'd put up query here to get one last confirm before moving ahead as there maybe someting about my configuration of monitors, or my planning to use both graphics cards that will catastrophic.

Comments will be greatly appreciated.

GTX 680 or

Thx for suggestion. I'm a bit reluctant to invest that much in a 6+ year old machine. I can get the GTX 650 for about 10% of the cost of a GTX 680.

Yosemite & Spaces

Thx for comment and reference. I tried spaces on Yosemite, but could not create the same multi-monitor setup that I have with Lion and understand that I will have with Mountain Lion (when I get my machine back from repair/files recovery).

I have four separate spaces and can have all monitors on the same space at the same time (same background, but independent displays on each monitor). I was not able to reproduce that environment on Yosemite.

End of story

GTX 650 arrived with extra(separately purchased) power cable. Installed in first two slots, then added the Radeon 2660. Main monitor connected to Radeon with other two connected to GTX 650. Mountain Lion comes up with "smiling" apple when booted and all three monitors run happy.

By the way, the net cost on the GTX 650 (after rebate) was $59.95. The power cable was $7.99. Got everything thru Amazon.

Thx to all the threads that helped me through this upgrade. Now I need to add some SSD and figure out how to get Fusion going with Bootcamp so it doesn't damage my existing Windows that I run in native mode.