I would opt and get the ProCal. The dealership will typically charge to recalibrate for larger tires. As for hand calculating, You will need to find the percentage difference between the stock tire size and current size and remember to add that to the miles traveled before you calculate. I usually have to add about 17-20 extra miles when I hand calculate since I havn't corrected for tire size yet.
2010 JKU - Stock for now
2005 WK - 6" lift, 35" BFG's, a lot more (SOLD)