If a person is strictly hunting deer, I'd suggest a good 180 grn JHP loaded to full power 10mm = 180 grn @ 1200 - 1300 fps.
Was I going after hogs and or black bear I'd perfer a 200 - 220 grn hard cast lead bullet with a flat nose @ 1200 fps or so.
In some states, such as where I live, people are required to hunt large game with JHP or JSP bullets. 
That being the case combined with the fact that I don't know if I might end up running into a buck, hog or big black bear - I will be hunting with the Underwood 200 grn Nosler JHP load this fall in my Gen3 Glock 20sf.
When carried as back up to my rifle I'll have the stock Glock barrel in it, if I am hunting with my handgun only I'll have a 6" Lone Wolf barrel installed to get an extra bit of velocity from the ammo.
Hope to have some pictures and stories for you guys soon............
Take Care and best of luck to all you 10MM hunters!!!

Your Glock 20 Long Slide sounds like a great hunting handgun & GREAT handgun to have working / living on a ranch.  It's all in how you carry it, personally I would find a holster set up that would work for you.
Recently I shot a Glock 20 & Glock 29 side by side with 3 different types of ammo.  The G20 handled them all with ease & they were comfortable for me to shoot.
However with the G29 when I shot a fairly mild 200 grn load, the gun started to move around in my hand noticably.  My hands are large (I wear an XL size glove), the mags had grip extenders & I have been shooting magnum handguns for many years.
My point is, even though the G29 would obviously be easier to carry, I think you'd be disapointed in your ability to shoot it as well as the G20 long slide version you have now - especially when shooting HOT loads in the G29.

Bottom line, Keep the G20LS & find a holster set up that will work well for you first.  Then if you still want to, save up and get the G29. 

Do you still have the 124 pieces of 10mm brass for sale??

If yes, I'll take it.

Looking at this thread made me feel good about the deal I got last fall.........
Picked up a S&W 1066 w/2 factory mags, everything looked like new for...................$500.00

Achall29,
Did you ever get a response to this Want To Buy posting here??  I see no one posted a reply, but that doesn't mean they didn't email you directly.
Just wondering because, I was thinking about getting a 6" barrel for my new G3 20SF, was hoping to find a used one for a bit cheaper than they are going for new.

All sold out, at this time.  Hope they have more soon!!  I'll be checking back...........
Thanks for the tip.