I only use my Orbital for 5x4 negatives. For B&W prints, I don't think I would worry about a 2 degree difference. I never measure the temperature of my developer when using normal trays.
For black and white I would always process at room temperature. The paterson Orbital was originally intended to be used for processing colour prints where temperature is more critical so I think the calculator is only really valid for colour.
However, I will have a look tonight to see if I have my instructions. If I can find them, I will post them.