So Keith, what is your targeted species? Thistle, burdock, or tall grass? Sumac, honey suckle, or other 1"-3" wood? What cutter head do you plan on running? The great thing about Stihl products is that there are many cutter and gaurd options available, with complete interchangeability from FS 90 to FS 350. I've used an FS 450, KM 130R, FS 80, and FS 66 R on my place to do all of the questioned tasks. I've found that when running a bike handled clearing saw through a stand of small trees it is nessecery to have an assistant clear the cut trees from your path. I've found the '130 R with loop handle to work well on saplings if I'm by myself and have to clear my own path as I go. When running the three or four blade grass knives, or poly cut, I've found max horsepower is not always needed. It's not like I'm going across an entire waist high ten acre pasture though. The FS 80 works good for me with poly cut, keeping the thistle and burdock down. I never really like to hold my equipment at WOT while not loaded. And it's not easy to keep a consistent load while brushing. For this reason I prefer the Stihl '130 motor for running between half and full throttle. The 4-MIX just seems to have so much more torque and response around half throttle than its two stroke counterparts. The A/V system of the 310 looks nice, and is definitely appreciated on a long outing of trimming. On my FS 80, I have the deluxe harness, but the vibes still get to me at about 1 1/2 tanks of fuel.