GeForce now seems pretty reasonable at max settings, provided you are close to a datacenter. I need to play around with it a bit. My primary system is a iMac 5k (though I usually play on a 1440p secondary monitor), and other than the annoyance of having to play at 1080p (which don't get me wrong, is annoying as hell!), the service is otherwise entirely playable on max settings.
I can't dual-boot because this iMac is also my media server and work machine, but it looks like I can run GeForce now on my second (2k) monitor and have similar performance to what I was getting natively. Not bad for $5 a month I guess if I have to do _something_.