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HD7950 or GTX670. 7970 + 680 = Waste of money.
A waste of money is a little strong but for the extra performance over a 7950/670, some people feel, doesn't warrant the extra spenditure. a 680 Vs a 670 would only be noticable with a fps counter running. You wouldn't notice without and the same for the 7970/7950.
If you want a 680 or 7970, go for it. The guys are giving their advice (of which is good advice) and showing how you could save a few pounds.
Knowing what I know now, I would still go for the MSI LTG 680's or the MSI Lightning 7970's but that would be me knowing I am spending far more than I need.