The main problem with any calculation is it will be wrong tomorrow.

The price varies every day and the difficulty varies every 2 weeks.

The biggest winners this year are those mining last year with new equipment back then, that didn't switch off and sell their hardware due to such calculations.

The main point would be to not pay ridiculous high prices for miners, and ensure that your elec cost has a good expectation of being covered for a good distance into the future even if the price isn't much higher and also if the diff does go a lot higher.