Don't mess with low voltage RAM on a Z77 build, you will need 1.5V. I'd also consider dropping the SSD and then investing the difference in upgrading to the Radeon 7950 and a stronger power supply. Otherwise everything else looks good.
I am a big proponent of the SSD drives. Your original build included an SSD and I would recommend keeping it. It will noticeably improve your boot times and will enable faster loading of new levels for your games. The downside is they are small and you won't be able to install many of your games on it.
Yes, an ssd would be nice, but in the end is pretty much irrelevant if he is looking for the best performance for gaming on a budget of around $900. If you could fork out the extra money an ssd is a welcome edition to any build as it will drastically increase boot times as atomic states, however boot times on a conventional 7200 rpm hdd should not bother you too much. Cooler master is a good case and I would recommend it, but their are easily several competitors you could substitute it with minimal price difference.