I often write out the pros and cons, weight them, do out the calculations, and then ignore them and go with my gut instinct.

There's some evidence that this is more effective than going strictly with the numbers. Our unconscious minds are often able to process more information than our conscious minds are: there're details that we're aware of, but don't know that we're aware of. They get missed in the calculation, but get included by a gut check.

The reason for writing out all the pros and cons, even if you throw them away later, is to force yourself to think about all the relevant facts that you can. There's a difference between issues you've never thought about and issues that you've thought about but can't hold in your head all at once. Plans are useless, but planning is essential.