For those that have tried this driver that choose to replace the shaft - do you try a replacement shaft based on your experiences with other driver heads from other OEMs? For example, my current driver is a Cobra Speedzone Xtreme with a UST Mamiya LINQ Gunmetal F4 shaft. That combination of head and shaft is working well for my swing (though it's taken some time to get there). If I were to demo the BB21 and don't like the stock shaft would I consider the current LINQ shaft I have (which would have to be re-tipped for the Callaway head) or guesstimate an equivalent shaft based on the specs of the LINQ? I should also add that my current combo is a tour length shaft playing at 44.5"...