Problems with 5870 & 5770 for Maya?

Question

Hi, I have a 12-core 2.93GHz Mac Pro and need to add another monitor.
So right now my current set up is a 24" ACD, a Dell u2311h, and some 1080p TV running off a 5870. I have heard that whenever you add another monitor, in cuts the amount of video RAM your GPU uses for each monitor. And because of this, I only plug in the TV cable when I want to watch a movie or need to show something on the TV.
I am wanting another Dell u2311h and will need another GPU. I am looking into the 5770 because it is only $250. I do a lot of Maya work and the added screen would be extremely helpful.
Whenever I am on Maya, the viewport is always on the 24" ACD, and I have all my other windows spread out across the u2311h. The main windows I will have open on the u2311h are nothing GPU intensive such as the outliner, hypershade, UV texture editor, light linking, render view, and a few others.
And because I heard that when you have multiple monitors running off 1 GPU the video RAM is cut in half or thirds, I would like to have the two u2311h's running on the 5770 to keep the 5870 just for the viewport.
I am wondering if this will cause any problems. Will Maya get confused by having some windows running on monitors from the 5770 and the viewport on the 5870? Would going from 2 monitors on the 5870 to 1 on the 5870 provide any performance increase? Would having 3 monitors (u2311h X 2 & TV) on the 5770 for the non-intensive windows cause any problems?
Right now I just do not want to have any performance hits by adding another monitor. So if I would have some performance hit, what would be the ideal setup for Maya with a 5870, 5770, ACD, 2X u2311h, and a TV?
Lastly, I am currently under the impression that I will need a small external power supply to do this. Both optical drive slots are filled and I am perfectly fine having an external power supply on top of the Pro and a wire running into the pro from the top PCIe slot. What power supply would you recommend?
Or would the regular power supply be able to power both GPUs if I use this cable?
Thanks in advance for the help!

Answer 1

I have a Mac Pro early 2008 (3,1) with two display cards - an ATI 2600 HD (came with the computer) and an Apple branded ATI 5770.
All was reasonably well until I installed a Sonnet eSATA card in PCIe slot 4.  Then,  roughly every third time the computer went to sleep it would not wake up - the same problem you had.  I had to reboot.
Unfortunately, I could not find a solution and I removed the eSATA card.
You do not have that option.  So, my only suggestion is that you do as you suggest, and turn off sleep.  Keep in mind that "display sleep" and "computer sleep" are different things - you may be able to get away with disabling computer sleep in system preferences, but keeping display sleep functional.  This will save some power, and will turn off your monitors, but the computer will still be awake, and would probably respond to a wake signal (like a keystoke or mouse click)