I'm playing on a 27" iMac with 3.4 GHz Intel i5, GF 780M GTX, bootcamped to Windows 8.1. This is well past the recommended requirements, and I'm generally getting really smooth framerates. Graphics setting "high."
However, whenever someone casts Chain Lightning (e.g. adra beetles), the game turns into a slideshow until the FX finishes. I don't have a framerate indicator up, but I'd eyeball about 2-3 FPS.
Not a huge deal, but nevertheless something that should be addressed.