You can also try a 'trial' version of 4k using DSR, the performance should be similar.
If you are talking about games from before 2010, there shouldn't be any problems with reaching at least high setting on 4k (there are some I was able to get 4k with playable frame rates with games later than that, for example Mass Effect 3).
(DSR is one of my main reasons to not go 4k 60hz screen).