Agree with the others go stock!
For Underwood ammo, which is a great product, I would stick with the 180 grain loads. Their 200 grain XTP is loaded very hot, thus with this particular load you might be better off with an aftermarket barrel that gives more support for the case.
The stock Glock barrels are designed for ultimate reliability, and the Underwood 180 grain loads are plenty powerful enough medicine for what you need them for.
Congrats and enjoy!
"...the men under your command deserve your leadership."-OXCOPS