I'd only worry about the life of that 470! It's a second hand one so you dunno exactly how old it is. I had a 470 for about a year and a half and it started showing its age in many games. Temp's also shot up to around mid 90's and sometimes even 100 (I am aware that its built to run hot and the threshold is 105). In its earlier days, it would stay put at 85. I did the usual stuff (cleaning out the dust, etc) but it didn't really help much.
I'd say go for the new 560. Better architecture, runs cooler and takes in lesser power. Or if you can throw in some more bucks, the 570.