I tried high, but let the screen go dark. I thought it was bricked! Not very responsive.
I think you have to keep the screen on.
Medium should work fine. If you are using the phone, you could set it to low if it is going too slowly.
You won't make much. I would be concerned about long term effects on the phone.
Let us know if you give it a go. I would be inyerested in hearing about it!