Also, if you're serious about 10mm backwoods ammo, click this link:
http://www.doubletapammo.com/php/catalog/index.php
15 rounds of that in the mag, and one or two more 15 round mags on your person is prolly, pound-for-pound, one of the most competent self defense tools you can find anywhere.
If you have any specific questions about the 10mm, or the G20, just ask in this thread, or wander over to
http://glocktalk.com/
The 10 ring section deals with the 10mm round, and I bet just lurking around in there would answer a lot of your questions...
Also, there are a lot of useful little gadgets available at:
http://www.glockmeister.com/
http://www.topglock.com/index.html