The resolution depends. If u use 1920x.... then u dont need to blow a whole in your pocket for 2 470's. A 460 1gb SC will do just fine. SLIing with the 460's are so so close to a 480 that the 470 isn't really seen at that point. (Check reviews on the internet for proof.)
So my advice it to get 2 460's.
but for 2560x..... resolution if u want really good frame over 25fps in every game with highest setting and 4xAA or higher u would wanna get those 2 470's IMO to get that extra juice. 480 is waste of time completely and they produce alot of heat and those extra heat pipes on the outside will push more heat into ur system.
well i have a 27inch Full HD screen, so what ever the max resolution i could get and i want to have maximum performance possible...
so what your saying is the $80 is a waste and is over priced and two 460's is more efficient and will provide less heat into my system