Maintenance for the week of November 25:
• [IN PROGRESS] Xbox: NA and EU megaservers for maintenance – November 27, 6:00AM EST (11:00 UTC) - 9:00AM EST (14:00 UTC)
• [IN PROGRESS] PlayStation®: NA and EU megaservers for maintenance – November 27, 6:00AM EST (11:00 UTC) - 9:00AM EST (14:00 UTC)
My take is that iMacs with their dedicated graphics cards in some models (especially the 27" models with BTO options), and their larger form factors, which allow for larger thermal budgets and thus higher (base) clock speeds in both CPU and GPU, have a significant edge over the MBPs.
Comparing the current models, anything but the highest end Macbook Pro is using integrated graphics. Any current iMac will wipe the floor with them. Unless you're paying top-dollar, you're probably better off with any of the iMac models for gaming.
That said, the highest end MacBook Pro has an M370X in it. Now, that's still slower by about 50% than the M290 or M290X in the current iMacs (and the high end iMac can be configured to an even better M295X…), so when running at the same resolution, you'll end up with the iMac being almost twice as fast. BUT… You'll rarely run the two at the same resolution. The 15" MacBook Pro screen is only a native 2880 x 1800 whereas the 27" iMac is a whopping 5120 x 2880, which means it's pushing roughly 4 times the pixels on the iMac. So in native resolutions, I'd expect the iMac to actually have a slightly slower framerate than the top of the line MacBook Pro.
So if you're willing to pay the price it's a tradeoff -- higher resolution rendering on a really nice screen at a slower framerate, or a much smaller lower resolution screen with a slightly higher framerate… but which is portable.
Practically speaking, however, until the new client with OpenGL 4.1 support comes out, neither one will be performing at their best, IMHO.
It really depends on what you want to do. For role-playing anything is good enough that gives you more than 10 FPS.
For PVP even the current top of the line iMac 5K and settings to low (at at a reduced screen resolution) is NOT good enough for competitive fights
This is due to the fact that ZOS will sent out your keyboard input only with the nextframe refresh (vertical sync is your enemy), then waits on the response from the server (server and network latency) and only then when it finally got return packet will the client calculate the outcome for the upcoming frame.
As example (assuming same network / server latency of 50 ms)
Windows gaming rig with 150 FPS (even in heavy combat): 7 ms + 50 ms + 7 ms < 75 ms
A current Mac with 20 FPS (i.e. under heavy PVP load): 50 ms + 50 ms + 50 ms > 150 ms
The input from the Mac is (at best) still in the queue server side, when the Windows Gamer has already got his damage out, interrupt through, shield up, healing done, etc.
In short, the (completely unnecessary) additional frames per second latency willkill you any time you happen to fight against someone using a windows based gaming rig. (add to that that macros are easy as pie under windows, which only makes matters worse)
So unless you can bump up the FPS >> 100 FPS, stay out of PVP or get used to dying a lot.
Therefore, even with an AMD Radeon R9 M295X (4GB VRAM) ESO (PVP) is unplayable given the current client / implementation of syncing user input & packet processing to the frame refresh rate and no global cooldown on skills & animation canceling.