It gets more complex when you are at 100 units. That is 66 dollars a day.

You could risk running at turbo until one breaks.

35 x 66 is about 2200. So every 35 days that extra profit pays for 1 unit.

So if 1 or 0 units break in 35 days it is a win or a push.

If  0 or 1 units break in 70 days it is a win.

This part of the you have to have money to make money.

100 units is about 200k worth of miners.

I know of a few people with 20 of these. They do normal speed with 4 cent power.

Down the road they will bump to turbo.  Since 20 earn them about 160 a day.  In 30 days they will earn 4800 that means 2 of the 20 are paid off.  They will know of the risks of turbo and will have at least paid off 2 units.