GPU fot OpenCL

[Stratoukos]

I have an early 2008 Mac Pro and I've decided that I want to learn about OpenCL programming, so I'm in the market for a new GPU. Since money is an issue, I want to buy a retail GPU and flash it to avoid the huge markup.

The GT120 and GT130 are not available outside Apple where I live (Greece) and the GTX285 is way out of my budget, so my options are either a 8800 or one of the ATIs. Currently I am leaning towards the HD4870 but there are two issues.

Firstly, I am not sure if a flashed HD4870 would be able to run OpenCL programs. If I understand correctly the flashing process there shouldn't be any problems, but I've heard that the Mac cards have a slightly different instruction set from the PC cards and this could potentially mean that I couldn't run some OpenCl programs.

Secondly, I've heard that the ATI OpenCL drivers are of somewhat beta quality. There are some posts here about the HD4870 not being able to run Apple's sample programs but they are some months old. I don't care about performance, since it's a rather academic project, but I want to be absolutely sure that the GPU is 100% OpenCL compliant before making the purchase.

So what's your advise. Should I buy the HD4870 or the much older 8800? Or should I shell out and buy the overpriced GT120 just to be 100% sure?

PS. There is a mix of Hardware and Programming questions here, but since it's about a GPU purchase I decided to post it here.