What tool or kernel are you using for overclocking? I'm running CM11 M8 on my Tate, and the built-in performance settings only let me go to 1500MHz for the CPU and I don't see any GPU overclocking options.
Although I will say that even just running CM11 at 1500MHz seems substantially faster than running Amazon's stock at 1200MHz, including for games, so I don't know what OP is talking about. Granted, he was running a nightly from several weeks before the M8 snapshot, so he could have just been running into some bugs.
You have to flash the linaro kernel for cm11...you can find it in these forums and should be able to flash from twrp