Well, the thing is, you have two power cords and probably 2 slots free.
So you have to balance between money and performance.
The best possible solution is a Dual Quadro 4000 config.
Thats 1500 bucks.
The benefit is, you also have a card for Adobes Mercury engine, games, Smoke, Cinema 4D, Scratch, Mocha Pro and all other apps depending on OpenGL and/or CUDA.
For a Resolve only station, you just need any Apple certified single slot card and add an old GTX 285 or a new Quadro 4000 or endofline Quadro 4800.
But your ATI Radeon HD 4870 is dual slot, right ?
So the Quadro 4000 is the ONLY option if you want to keep it.
A slice of color…
DaVinci 7.1.2 OSX 10.6.7
MacPro 5.1 2x 2,4 24GB
RAID0 8TB eSata 6TB
GTX 285 / GT 120
Extreme 3D+ WAVE
http://www.saschahaber.com