I have a 680 at home, and I do a fair bit of work in both Soft and Maya, not to mention CUDA, that is tightly tied to the videocard.
I definitely got slapped in the face by the crippled double precision issues in some of the CUDA work, but I can say that once I had a decent driver/config combo down it was matching or outperforming by far the (f)4000 I use at work for in-app stuff.
I’m not a benchmark monkey, so all I have to offer is personal, but of actual usage scenarios.
Maybe presumptuously so, I also think that after writing enough CUDA deferred eval nodes in both Maya and ICE, not to mention performance testing the same things at work and at home, I would have noticed if the 680 was such a truly crap card 
Mudbox, Mari, Topogun and vegas GPU effects also all respond well.
As I mentioned in past threads, I have heard that rumor, repeatedly, but never from anybody I know, and I personally haven’t encountered it.
I can’t promise anybody a 6xx will be fine, because there’s statistical evidence it might not be according to the internets. I can say it might be worth at least trying, and doubting that those rumors still hold true, based on personal experience though.
The above also all holds true for my girlfriend’s Asus laptop with a 6xxM (tempted to say 650).
The artificially cripped DP issue though is very real, as is the usual ID/driver sham that are quadros, as proven by the hardware hack conversion of a 680 into a full kepler quadro I posted not long ago.
