Difficulties, Vardiffs, etc - Help Needed!

[citronick]

I have the following ASIC miners and would like to optimise hashing power, sound and heat reduction - hopefully for best mining returns on BTCs.

Below are the configs optimised for least sound and heat, with best possible hashrate.

1. Antminer S5 at 400 Megahertz with default password, current fan speed 3960RPM, each ASIC board with 52-54C average. Stock firmware but default was 350Mhz.
2. 2 x Antminer S7 at 600 Megahertz with password d=42838, current fan speed at 50% running 3720RPM and 3600RPM, each ASIC board with 58-61C average (day), minus 3-4C at night. Firmware installed is the 600Mhz version. The S7s are very loud when running default settings.
3. Innosilicon A2 Terminator 110MH at 1250Mhz with password d=42838, current hash average 115MH, fans speed steady but not as loud as default password.

My questions:
1. The higher the difficulty, the less strain on the miners (SHA256 or Scrypt for that matter), therefore the fans don't speed up and generate less heat - is this correct understanding?
2. Assuming that the higher the difficulty set for the miners, achieving the above #1, the payout rewards are also higher for solving difficult algorithms?
3. What is the optimum d=xxxx for A2 110MH and the S5 and S7s? Is there a table updated given the BTC and LTC network difficulty in November 2015?
4. What is the highest expected BTC return for my setup above?

Any other advise or improvements highly appreciated. All the mining equipment are bought mid-2015.

Thanks guys

TMT

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[achow101]

My questions:
1. The higher the difficulty, the less strain on the miners (SHA256 or Scrypt for that matter), therefore the fans don't speed up and generate less heat - is this correct understanding?

No. AFAIK the difficulty does not matter regarding the speed at which the miners mine and the power they use. The miners will mine at a set speed and simply have to do more work to find one solution. In a given amount of time, the miner will do the same amount of work, just that with different difficulties, a different number of solutions will be found.

2. Assuming that the higher the difficulty set for the miners, achieving the above #1, the payout rewards are also higher for solving difficult algorithms?

No. You will actually be paid less. Since you are doing more work and spending more time on one problem, you will be submitting less solutions (shares) than with a lower difficulty. Since most pools pay in some way related to the number of shares submitted in a given time period, you will be paid less since less shares are being submitted.

4. What is the highest expected BTC return for my setup above?

I don't know, but there are many online mining profitability calculators out there. Do a google search for them. Usually you will need to enter the hashrate or the hardware model (it will know the hashrate based off of the hardware), the power consumption (again it will know the power consumption based off of the hardware if that is entered), your power rate, and the amount of time.

[-ck]

Suggestion for how to choose a pool difficulty for miners:
https://bitcointalk.org/index.php?topic=274023.0