Crysis 3. "Welcome to the Jungle" level, specifically.
It's always my benchmark / testing level. Pushes utilization on all my CPU cores and GPUs and generates more heat than any game I've played so far.
I think it's important to quantify "graphic intensive." A lot of games present engine bottlenecks or code issues that result in poor performance (ArmA comes to mind). That's not what I would consider graphic intensive, that's just difficult to run.
I think Witcher 2 is pretty easy to run (even with older GPUs), as long as you leave supersampling off. To be fair, now that NVidia has enabled DSR, you can do the the same thing with a lot of games. It's not really a graphics quality issue, it's a resolution / downsampling setting, so I wouldn't consider use of that technology to be relevant in determining how graphically intensive the game is to render.