These are the specs I am currently running with the game on my iMac.  If I set it on Ultra it is by far the best the game looks on any other system that I currently own but will crash frequently.   Even if I set it on High or Medium the game still crashes.  Cyrodiil regardless of it having a high population or low population is where I crash the most.
Imperial City surprisingly is ran very well and I have very infrequent crashes there.
PvE areas its very infrequent but will crash randomly.
•	3.4GHz Quad-core Intel Core i7, Turbo Boost up to 3.9GHz
•	8GB 1600MHz DDR3 SDRAM - 2x4GB
•	1TB Serial ATA Drive @ 7200 rpm
•	NVIDIA GeForce GTX 680MX 2GB GDDR5
I have tried running the game with Viola to record my game play and even attempted to try and stream on twitch.  Both seemed to bog down the system enough that I could play but not very well.  I know very little when it comes to Mac but wanted to throw out my systems specs to see what I would need to be able to stream and or record gameplay comfortably.
Any advice on settings or things to look at for the iMac to assist with smoother better gameplay I would love to hear it.  I will be testing out a new PC for ESO as well and will be uploading my experience with it as I progress.  I do however love playing this game on the iMac as it is truly the best the game looks!