i took the benchmark data people posted here: viewtopic.php?f=21&t=996&start=0
and put it into a spreadsheet https://spreadsheets.google.com/ccc?key=0AvzT-1kiffQxdFFZQUREd09aUzFwd1pmeUJhYlVUb1E&hl=en&authkey=CIretpwP
I looked up prices on newegg (or google shopping if not found there) and charted performance alongside cost effectiveness (the units being $ per megasamples, multiplied by some unknown constant :)
the 480 is "theoretical" because it seems no one tried it out before switching to a new benchmark on a different thread. it's based on Radiance saying the 480 is 1.2x faster than the 470.
anyway - my quick analysis is that 260's are the best "deal" - assuming that the 470 overclocked post is an anomaly. thoughts?
PS: feel free to point out the probably dozens of flaws in my logic & my spreadsheet :)
Mac OS X 10.8.0 | ASUS GTX 580 1.5GB | MSI GTX 470 | ATI Radeon 6870 | Core i7 2.9Ghz | 16GB