Help Replace ATI 5870 in MP (5,1)

The stock Apple 5870 in my upgraded Mac Pro 5,1 (really a 4,1 with a single 6 core 3.33) seems to be failing and I'll need to replace it in the near future.

I don't/can't pay for an original 5870 replacement and the less expensive 5770 may even make less sense. Here is what I'm looking for:

1) performance similar or better than the 5870. In reality something performing like the 5750 would probably be fine, but I assume not cost efficient at this point? I don't need super high FPS in any sort of gaming scenario. My main uses are Aperture (for a bit more), LightRoom, Photoshop, iMovie, Final Cut Pro and a few other related apps. Obviously it must be rock solid in terms of stability.

2) the capability to drive a 27" Apple Cinema display is absolutely needed. Ideally if it can also drive the speakers over Mdisplay port -- all the better.

3) If the card can also drive a future 4K display -- great!

4) Boot screen is not required -- I don't bootcamp, and even if I decide to a reboot is fine by me.

5) If I can be kind to both my aging MP's power supply and the environment, awesome! Not sure what the best metric is for Bang/Watt, but it would be very cool to make use of better tech to make my graphics card work off of one power lead and not two, like my 5870. I really hate to see that the video card often uses as much power as the entire rest of the computer.

So, love to hear your recommendations.

 

Arggggghhhh.... Thanks for the heads up! Moved post to correct sub-forum.