You said in your original post that you wanted something roughly equivalent to your D7; It would take something in the 20-ton (320-200) class at a minimum. A 6 or 7 ton machine would be much less powerful than a D7.
Pound for pound, I'd consider an excavator to be a more capable clearing machine than a dozer. Still, as you say, I'd consider a 7 tonner to be a toy next to a D7.
For clearing substantial trees from forest and fencelines, you'd need at least a 312/120 size machine to be productive. A 315/160 size machine would let you tackle almost any job. Beyond that, bigger is better in terms of productivity, but there are few jobs that absolutely need the strength of a machine bigger than a 315.
I've got a 200 John Deere, and even then I sometimes wish for a bit more strength when pulling stumps, but I've never come across a tree hereabouts that [with patience] a 315/160 size machine can't tackle.