I'm sure this will sound a tad arrogant, since it's you we're talking about, and you know you, but I'm of the opinion that your successes in life since leaving the witnesses (such as running marathons and taking an active assertive role in various things) have probably done as much or more for your speaking ability as all your years as a witness.
I hear this argument often, from ex witnesses and witnesses alike. But I think they'd be good public speakers anyway. Yes, the practice doesn't hurt, but the theocratic ministry school format sucks for just about anything more than just that, practice.
I sucked as a public speaker from my first talk to my last talk. I knew it, they knew it. That I did good research (well, for a witness) and took a slightly interesting "angle" on the topic at hand (well, again...for a witness) was a relief to those who felt the need to pat me on the back... they didn't have to lie and say my delivery was any good, lol.
Relatively speaking, I could go into a KH and kick ass in delivering a talk today, as compared to when I was a witness. I've found that I am less nervous in front of an auditorium of strangers, asking questions of a famous person, or even being interviewed for a TV show that I knew would be seen by millions, than I was in front of 15 people in the "second school".
Just my take on it.