I have been clearing overgrown land full of briars, vines, scrub trees (3-5 inches) and a few big trees per acre. I actually timed myself over the summer using the combo of bush hog, grapple, 21hp tractor, chain saw and finally a backhoe (traded out with the bush hog). I could clear the land at a rate of a third an acre per 8hours not including going back for the stumps. I ripped out a lot of the trees whole with the grapple so I had about 20-25 moderate to small stumps and a couple of big ones per acre. That takes another day and a half approximately with the BH. The whole clearing process ends up taking about 4-5 days per acre with my equipment and leaves the land covered with mulched stuff from the bush hog but otherwise ready to move on to seeding (except for still needing to fill in some stump holes).
I'm sure a dozer would have made quicker work of the project but 5 days work per acre cleared seems pretty good considering how long it would take without a tractor or the right implements. I could not have done it nearly as fast without the grapple and could not have managed the moderate and larger sized stumps without the backhoe.