Is the 5670 a good OpenCL platform? Would it be a decent card to upgrade to if you are unhappy with the poor OpenCL support with the 4850?
http://www.informationweek.com/news/security/client/showArticle.jhtml?articleID=222301003
i think 5750 is better option. 5670 can have lower performnace than 4850.
I would go with a 5770 ... over the 5750 or the 5670.
It has double the stream processors of a 5670 and more than 10% higher clock for less than twice the price. Its has more than 10% more stream procs than the 5750 and also a 20% higher clock for about %15 increase in price. It is like a 5870 with half the processors (same clock, just no double precision support, which I guess most don't need) and 2 5770s are easily cheaper than a 5870. For GFlops/$, I think its the sweet spot.
http://benchmarkreviews.com/index.php?option=com_content&task=view&id=441&Itemid=72&limit=1&limitstart=6
But wouldn't the 5670 at least let you use local memory, unlike the 4850?
yes you could use local memory. but you get in fact downgrade in computing power. thus i recomend at last buy 5750.