I have a tank of similar size, 850 high x 830 wide x 550 deep. My depth is quite a bit more. The depth and correct lighting has been a challenge, I currently run a 150W MH with 2 x 24w T5's, am upgrading in the near future. The problem I forsee you having is spacing a reef with your depth, my depth of 550 has allowed me to aquascape quite high and still be able to keep Zoo's and softies at substrate level with some SPS on top.