I don't think I could ever go back to HDD. the 680mx is performing better than a 675 so you are going to see even worse performance in your benchmark which in turn will make you feel worse. If you didn't care about graphics you wouldn't be benchmarking it right? There is also the fact that if you have a flawless machine, swapping it for another version gives you a chance of receiving a flawed machine
You're running ultra settings, 8xAA, and are benchmarking in OSX. In OSX I get around 39 FPS with standard presets in 1440p native resolution and under windows it's something over 50, without overclocking.
Besides that, the 680MX runs Crysis 3 with high settings smoothly at 1440p, other current games even run with max details. It's a great GPU, the best ever available in an iMac and still currently the most powerful mobile GPU. With some overclocking the 680MX is between a desktop 660ti and a 670.