Absolutely the best caliber for goats is THE ONE YOU HAVE THE MOST CONFIDENCE IN!!!
Don't be afraid of bringing out your '06 or whatever. I have shot them with 7mm Mag and .300 Win Mag. The falacy that "a big gun will not leave any meat" is absolutely untrue. I used to bellieve that (to a point) until I saw what a .338 Mag did to a Mule Deer. Punched a hole in both sides with no more damage than a .243!!
The biggest issue for guys from back east coming out here to hunt lopes is you need to practice 300+ shots. Alot!! Know your round's balistics (bullet drop at various distances.) I have even taped a cheat sheet to the stock of a rifle. Also, bring good, powerful optics including a range finder that is good to 1000 yards. No sence in knowing your ballistics if you don't know the distance!
And practice, practice, practice. Lastly, punch a few holes in paper when you get here to make sure it is shoooting where you think it is. The higher elevation and reduced air pressure will effect your bullets trajectory. Plus a gun/scope can get bumped in travel.