Re: Hot Rail
The best rule of thumb is to go with what sounds best to you.
The "general" rule is to have a hotter bridge pup. This is because the guitar is not as loud at the bridge and therefore the extra output balances with the lower output neck pup but louder on the guitar neck position. In turn this combo allows for a more balanced middle position sound. But these generalities aren't cast in stone.
I'm starting a partscaster project in a SSS strat configuration. I was thinking hot pups in the bridge and neck and a low output RWRP in the middle. My thought being I could get some nicer clean tones than a more traditional setup with three hot pups. Plus, I rarely used the middle alone on my last strat. Low and behold, SD has an Everything Axe set in this exact configuration.