It's all relative to the resolution and frame rate you're playing at. Some good bench 'weights' to examine with are:
1. 4k/60hz/10bit color-At the moment this tends be the toughest for most things out there. Even if you have a 1080p you can use DSR to get an idea of what it takes.
2. 1080P/3D/120hz-Believe it or not, this 3d res is almost as demanding as 4k. I have two different monitors and seen surprisingly similar fps between 3d & 4k.
3. 1440p/144hz-This is often considered the best combo at the moment although in the next year or so I'm sure 4k/144hz will begin to take the top. Many single high end modern cards of the last 2 years can do this as well as low-mid's in SLI/Crossfire and once you do, you don't want to go back.
Some good benching games for these are, and you can find many articles about them too are, and be sure to use the highest settings they have:
Doom(nightmare settings), Rise of Tomb Raider, Witcher 3, Metro's, Crysis 3, GTA V, Everybody's Gone to, Assasin's Creed IV, BioShock Infinite, Mordor, and the world's most horribly coded game but still great for bogging a system down: Batman AK.
Any of those at max settings on the above res combo's will give you an idea of your systems potential.
Some low usage games:
King's Quest, Dead Island, Dead Space, Transformers, King's Bounty, Alien Isolation, Mordor(surprisingly good at low or ultra), Bio Shock 2 or most games going back 3-5 years ago.