How many people use the Bonapane?
i only know of maybe 5 players in the country that use the bonapane grip full time on drives, but it was designed to get more nose down.
How much prospective distance am I losing (if any)?
you are losing 10-20% or more of your potential distance as that isn't a strong rip grip.
Should I just stick with it since I'm moving up to Grandmaster next year?
if you were having trouble getting the nose down with any grip, chances are you were not getting your weight forward and this was causing the nose up problem.
it's up to you whether or not you wish to address the source of the problem or to accept your solution to the problem.
What is the max distance that the Turbo can be used?
the longest turbo i've ever seen made was ~70-75'. this was with someone that had been playing pro since around 1978 and had been putting that way for 25 years.
How many people use the upside down putt in windy situations?
i've seen it done, but never really appealed to me unless the wind was over 45mph and the putt was inside 10'. i support it if you choose to do it because you feel it is the best shot. if it is what you do because of lack of confidence in putting it rightside up... im less supportive of that.
I'll be getting a DB5 soon....should I practice the more accepted forms of putting?
there's never really anything bad about adding more skills to your game. a very large chunk of people that putt with a more traditional style have some form of semi-proficient (at least within 10') turbo putt. i believe the reverse should also be true in that if you are a primary turbo putter, you should probably have at least a semi-proficient traditional putt.
however, since turbo putts generally leave pretty long fly bys on missed putts, i generally do not consider it to be a very high percentage technique unless you are willing to sink in MANY hours of practice.
based on the amount of experience you have with the sport, i would say buckling down into set patterns without having developed proficiency elsewhere is not the best decision to make just yet. it's one thing to have used the power grip for 10 years and decided the bonapane was a better choice vs. only being able to throw the bonapane. the same goes for turbo vs. traditional putting.