I was bored at work today, so I added a few things to an old spreadsheet I made back when we were evaluating mortgage payments. Maybe some part of it will be helpful to someone... I'm sure I don't need to qualify that it doesn't take into account ALL the factors of this decision - it's just a starting point for basic analysis. (Personally, I like the mortgage tab - seeing how early I can pay it off with extra payments). Just enter your assumptions into the yellow highlighted cells on the Assumptions tab and view the results on the other 2 tabs.

Chris