Correct me if I'm wrong but the way I see it is more TH/s is good?
So:
2x S7 = 16.2btc
4860 x2 = 9720
Current maintenance = 28.85%
9720 - 28.85% leaves you with = 6916 GH\s.

16.2btc @ S5 market = 20950 GH\s
Current maintenance = 58.49%
20950 - 58.49% = 8697 GH\s

Thing is I know S7 will last longer, but seems S5 will give more profit for longer?
I.E S7 needs to overcome the deficit of 1781 GH\s before it even started?

Thoughts?