From the Bitmain Forum:
S5 vs S7 Profitability - You heard it here first.
For everybody panic selling their S5 hash, I welcome you to put together some simple maths on the profitability between S5 and S7 right now.
Let's assume that you have 10 Bitcoin that you want to invest in Hashnest, and you're torn between S5 and S7. Here's the maths:
S7 Profitability
With 10 bitcoins, you'll be able to buy 5195 GH/s at the current price of 0.00192468.
Those 5195 GH/s will earn you 0.0429617 BTC per day, assuming 100% luck.
You'll be charged 0.01228772 maintenance per day.
Leaving you with a total PER DAY profit of 0.03067398 per day.
S5 Profitability
With 10 bitcoins, you'll be able to buy 13967 GH/s at the current price of 0.00071593.
Those 13967 GH/s will earn you 0.11550452 BTC per day, assuming 100% luck.
You'll be charged 0.06697278 maintenance per day.
Leaving you with a total PER DAY profit of 0.04853174 per day.
TLDR:
With 10 Bitcoins, buying S5 at today's rate will earn you 0.04853174 per day.
With 10 Bitcoins, buying S7 at today's rate will earn you 0.03067398 per day.