I drop a lot of trees in that size, and depending on the species and condition I'll happily go up to 5" or 4" diameter, as long as i see no signs of cracking or splitting on the way up. If its a tricky take down with no room for dropping and has to be taken piece by piece then I usually start from the bottom and work my way up, dropping branches as I go. I leave 5" of each branch attached to the trunk because it leaves me with steps and gives me more options rigging slings when it comes to taking down the trunk.
So by the time I get to the top, I've got a pretty clear trunk below me. I don't climb on spikes, so when I'm up there I use only rope and natural branches available. Even very small branches (1/2") will support your weight if you cat them back to within 4" of the trunk. I climb up as high as I'm comfortable with, then rig a really good sling round the trunk. So now you've got to top it. What I do at this stage is climb up as high as I can and take off every branch opposite the side I want to fell towards. You can really take off a lot! Then I get back down, get really roped in nice. Make my wedge cut. If I can drop the top straight to ground without roping then i go for a very narrow wedge, about 30 degrees. That way the top snaps clear early and I hardly even notice it.
If I have to rope the top then its different.... I go for a bigger wedge angle, but still not 90 degrees. maybe 50 or 60. I sling that top up real good. When dropping big tops, I use dynamic rock climbing rope that stretches up to 40% and absorbs a lot of the force of the fall. I get my groundie to leave a nice long run out so the tension takes up well below me, as much as possible. the lower the force takes up, the more the force will be directed downwards and not sidewards.
I use a friction device (usually a sticht plate) rigged off a top sling to help the groundie catch the top. To me there are 2, maybe 3 critical points to reducing rodeo antics at tree top. First is wedge angle. Too little angle, and you risk the treetop barberchairing. too much and the top 'kicks' the trunk sideways. there's a sweet spot where the top breaks loose from the holding wood and you dont even feel it. I think it's about 30 degrees. The second one comes into play when you are roping tops, and it's the point at which the rope takes up The lower the better for me. Too high, and the top is still vertical. It will take up, swing sideways and whip th trunk around. The third is the nature of the take up. Static ropes are horrible for big drops... but a good groundie takes up the tension in an elastic way. Try to pick rock climbers as your groundies if you can! They will take up the shock with their own bodies, almost launching themselves at the moment of takeup which results in a silky ride for you. Even better if you use dynamic ropes for topping, even better again if you use dynamic ropes with dynamic groundies ;-)
Shaun