It depends on the resolution and what you consider "maxed out." Technically, a true max out of a game in terms of settings must include maxed antialiasing. Even at low antialiasing, you will not achieve 60FPS for the more demanding games on the market at 1920x1080. A few of these games include Metro 2033 & Last Light, Tomb Raider, Crysis 3, Need for Speed Most Wanted, Far Cry 3, Hitman Absolution, Max Payne 3, Assassin's Creed 3, etc. Even with two GTX 660s, you would still not max a game like Metro Last Light with SSAAx4. In fact, you would need more than four, which is not even possible. My dual GTX Titans barely break 60FPS at SSAAx4 on Metro Last Light with Advanced PhysX and everything else turned up at 1920x1080. Don't pay too much attention to benchmarks, as they often have settings such as Advanced PhysX or Tessellation turned off or very low and they do not take note of this (Linus Tech Tips is infamous for this, never take their benchmarks seriously).
I would recommend a GTX 760 if you're looking for a cheap, but relatively powerful GPU. It's only $250 and you'll get almost as much horsepower as 2 GTX Titans if you grab four of them and throw them in quad SLI. The obvious differences would be power consumption, less vram, less memory bandwidth, etc.