I mixed up the power consumption, it should be 1.09 w/gh not 1w/gh when overclocked. It's fixed now and the tube is still the most profitable. It's ~$1700 more profitable than the sp31 in half the amount of time.
Each tube is ~0.96 btc each and can be overclocked to 920 gh/s at 1000W. A modded server PSU is ~$25 per miner.
Except that you can't buy less than 10 units for that price which makes your calculation impossible to get that hashpower for that price. You need to either raise the price or lower the speed, but I'm used to your misleading information.