Been playin arkham knight now for a while, loving it despite the horrible handling batmobile. I know a lot of people were upset with how the game ran but it's as solid as can be for me. At launch I couldn't even get it to start. But now, more stable and performed far better then fallout 4 which I put ~200hrs into.
My rig is old too. I7 2600k, 16gig ram, sandy bridge, sli 970's. Windows 10 Pro which was an upgrade not a fresh install. WD blacks using SSD cache drive. SSD OS drive. SLI ran like crap, but turned that off, dedicated my 2nd 970 as a physx card, turn on the 60fps option because 30 was a drag (were consoles locked at 30?) and with everything on max, all the nvidia stuff on, 1920x1080 ran PERFECT. Never an issue. Start to finish I had two crashes but honestly I think its because I left my security camera software running by accident.
Never paid a dime for the game, came with my gtx 970, but well worth playing through. Every bit as good as the others if not better.