I think something that needs to be addressed in this thread is your choice of holster, and where you carry it, and how that aids you in a "fast draw".
I carry strong-side, right behind my kidney in a very high percent of the time in an Askins style holster. I carry my primary in this fashion. I often, when using my mobility scooter, carry crossdraw in an IWB holster. The crossdraw pistol is actually a backup to my primary. I carry a Glock 99.999999999999999% of the time. Usually a G21 strong side, and a G30 cross draw with the spare mags for the 21 weak side. My mags are always in the same place, and will fit either pistol. I try to carry the smaller version of my primary...whether it is the G26 backing up the G19, or the 23 backing up the 22.
Carry your reloads in the same place all the time. I carry spare magazines for three reasons...in order of importance to me. The magazine is the weakest link in your gun. A great gun is of no value if the magazine fails. You just might need more ammo fast!. The weight of the two spares balances the weight of the gun on my other hip, and as a long time gun carrier...it saves my back!
I have acheived a pretty smooth and rapid presentation from the crossdraw position. As I have carried strong side for 20 years now...I am VERY proficient in getting that weapon into play. I still practice both here at my home range.
Use a quality holster. Use a quality belt made for carrying a gun. This is no place for a $9.00 nylon gun show special to be used as a tool carrier for the tool you MAY need to save your life. You will never become smooth, fast, or proficient with crappy gear. Carry in the same place. My hand goes to my stong side without even thinking. It goes cross draw if I am in my wheelchair or scooter. Muscle memory will take over when fine motor skills have gone out the window. You fight like you train, and poor training will translate into poor fighting.
I believe that a rapid presentation, while not always neccessary, is a skill that is best to have and not need, than to need and not have. Clint Smith said something to the effect that "The time to learn new skills is not in the middle of a fight."