Re: Will a Frontier 72\" finish mower handle briers OK?
My 2 cents...
I can't speak to the Frontier finish mower in particular, but I have a Woods RM660 72" rfm that I used to use to mow the fields, until I got new blades on the old no-name bush-hog. I've mowed grass that high with the Woods, and I don't think you need to fear damaging the gearbox or driveshaft, etc, even on those briars, if the Frontier is similar. However, I would take it very easy, make several passes, starting as high as I could, and take half passes. Most important, know what's on the ground before you lower the mower. The one thing that would likely damage the driveline or deck is a rock sticking up somewhere that you don't expect it. And since you're in PA like me, I'll bet there's at least one in that pasture. Even if there's not a rock, there's probably at least one groundhog hole with the dirt and stones piled up around it. That's the kind of thing you don't want to hit with your rfm!
I do think you should expect to prematurely wear, if not damage your blades, because they just are not designed for that purpose. But, blades are surely cheaper than a bush-hog. Also, if you want a decent cut with the rfm, you're going to need to keep the pasture mowed often and relatively short, no more than six inches mowed and about eight inches before mowing. That can get to be a drag if you're pasture is big, like my fields (5-6 acres). With the brush hog, you can let the field get away from you a little more and still get a decent cut.