Just my opinion but it varies by state, and even by area within each state. All I hunt is public land (except when Diablo invites me to SC
) and I find I can call more agressively to birds on public land in VA and WV than I can in MD and PA. Thats not 100% true all the time but it holds true more often than not in my experience. Having said that I agree with WVBOY; you should base your calling on each individual bird's response. Start soft and then give him more if he seems to need it, and when you find the right level then stick with it even if that means calling more than you expected.
I personally have always been more successful follow the "less is more" approach on public land, but I would never be afraid to crank it up if I think that is the right thing to do and I have had great success often in VA doing so. I would never hestitate to call more or more agressively if nothing else is working, even in high pressure areas.
One other thought; try a call that is out of the ordinary...i.e. wingbones, scratch boxes, single reed mouth calls, etc. Sometimes its that different sound that really gets em goin in pressured areas.
Good luck.
-Eric