Graphics Card needed, what's the latest?

I'm in real need to buy a new OpenCL GRAPHICS CARD for my slooooww FCPX.
I do pro audio n video and I have an 'Early 2009' MacPro 4,1 with 20 gigs ram
but it has a lame stock NvidiaGeForrce GT 120 card...

So what would you experienced pro's recommend 'these days'?
Ideally the budget would stay under $450 but I would go higher IF it really makes a big difference.

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Misc ?'s:
+ I'm leaning towards the AMD / ATI cards for the OpenCL compatibility but is it true that some Nvidia cards are now compatible too and might be a better deal?
+ Any thoughts on any just released newer cards - rather then the old Radeon 5870 with 1gig that everyone seems to get that is years old and expensivly priced at $450?
+ Is it really safe and worth the hassel to flash or tweak code to make a cheaper PC card work on Mac?
+ Ideally the card would work well with other pro media apps too...
(I've read that even Preimere CS6+ is/will be OpenCL compatible.. Resolve is also OpenCL compatible now.)
+ Is there a site that is current about Mac fcpx compatible cards?
(I sure wish fcp.co had an area for this topic.)
+ Any other issues I should be considering?

Edit - Update ?'s:
+ 2 new cards worth considering:
Sapphire 7950 and the EVGA 680GTX.

Thanks for any tips!,
freeform

I don't know about the other cards but I put the Radeon 5770 in my 2009 Mac Pro and got significant boost in performance and now FCPX almost never crashes. I run Adobe stuff on it with no problems.

Thanks for the reply ted..
Yea, the 5770 at around $250 is the most affordable of the bunch I've looked at.
I might have to get it with my budget these days and then upgrade to something better later... Hmmm, I wonder how much better the rendering/performance is of the more expensive cards to this in reality?

i have both, R 5870 and Nvidia 4000...all i can say is, Nvidia is the winner.
FCPX runs faster and it is more comfortable, timeline is smoothly.There is not an ocean between them and it depends how hard is your project (resolution/ effects..layers)

Thanks Vader.. my main concern is 'rendering' tons of plugins and titles etc... rather then scubbing the timeline smoothly (though maybe that's the same in the end).

The 4000 is over $1000 so that's out of the question 'for me' (but good info for others).
The 5870 is $450 and the main card I'm comparing to to see if there is something better/newer/cheaper.

I only have experience with the Radeon HD 5870 in a 12 core mac pro and it works very well, especially while driving (2) 27" LED Cinema displays. If you're only using one display, it should be even speedier.
I am not sure whether you can use those cards in your 2009 MacPro, but I assume you did homework to check that.

freeform,
I run a out of box ATI/Radeon 6870 in a MP1.1 and see vastly better performance. Only downside is no screen until log-in screen. I have the xfx brand ~ $180.00 usd. I got mine for ~ $160 on sale. It is roughly equivalent to the 5870 but half the cost.
The best site that I can recommend for GPU comparisons is www.barefeats.com
Rob et all run some very good tests. You can see all the major cards compared and with different platforms.
The 680 is looking good now.
Hope this helps, Greg
Oh, if you use a lot of Adobe software then get an nVidia card, helps speed up with cuda.