I'm using a 2012 MacBook Pro Retina (2.3 GHz i7, 8GB RAM, GT650M 1GB) and it seems that the performance with ESO under Mac OS X Yosemite (10.10.3) is really appalling. Previously, I ran ESO under Bootcamp with the same machine under Windows 8.1 64-bit with Medium (Resolution: 1920 x 1200) settings and I obtained FPS ranging from 40-70. However, under Yosemite, at the Lowest setting available (Resolution: 1280 x 800, Everything set to lowest or Off), and I can't seem to even pass 30FPS. Is this a know issue? Are there any workarounds that I could attempt? Currently I'm reinstalling the whole game to check if that alleviates the issue.
P/S: I removed my bootcamp installation because of the SSD space constraints and the fact that Windows doesn't support the Mac's Headphone/Mic combo jack thingamajig for the Apple EarPods. Also for some odd reason, the game only allows a max resolution of 1440x900 and even then I still can't get anywhere over 30 FPS and I'm also noticing thing like the blue wayshrine fire takes 5 seconds or so to load after approaching a wayshrine and once it's loaded my FPS will further plummet to 20-ish.
Also, I opened a support ticket (# 150527-000627) and they said that this behaviour is normal and should be expected and I found that answer to be rather unsatisfactory.