As the instructor told our class about grip as he prepared to teach us a handgun fundamentals, and I'm paraphrasing to the best of my memory...
The grip I'm going to teach may be completely different than the one you currently use, but just give it a chance. Every advanced school, police force, military and world class competitor uses this grip.
I can't say what grip I was using before the class. It may have been a modified thumbs foreword grip, but once I embraced the full thumbs forward, my accuracy and speed improved considerably. I'm confident I could not get to my current abilities with another grip.
Regarding competition. I know that jthhapkido will tell you that being a competitor will not make you an "Operator", but in lieu of testing such things on a battlefield, what better environment to test firearm techniques? In competition, speed and accuracy are king. You will likely need to shoot from all different angles and positions, similar to what is demanded of you in battle. I should also note that the Army sends competitors to USPSA and multi-gun competitions, and they use the same thumbs forward pistol grip.
Fly