I must say that I have been finding this topic extremely interesting. I have been doing draw boring thus far in the style of TIMBEAL, with the heavily tapered peg. I did this because it's what one sees really often with modern draw boring, identified by the space where the peg does not fill the back of the hole.
I had noticed when I have worked on old barns, as was pointed out earlier, that none of those pegs had a heavy taper, just the heavy taper on the last inch or so. Not having a very universal overview of old pegs I just assumed that they were outside the norm.
I really do like the concept of the full sized peg fully engaged in the peg hole, with any adjustment needed made in the tenon hole. That to me, just seems to be a more elegant solution. I'm sure that the draw boring that I have done up to now is adequate in function...but perhaps not ideal.
In view of this thread and the original question, it really seems to me that the heavily tapered peg would lose a significant amount of strength from loss of cross section and loss of parallel grain. The straight grain which is the whole rationale for riving pegs instead of cutting them from sawn stock. I figure that these subtle differences in practice will never make a difference in building longevity in our lifetime, but 200 or 400 years from now the cumulative effects make all the difference. There is a reason that for every ancient building still standing, there are countless others that have fallen in. It's a good reason to look to the survivors for best practice. I'm going to take a good hard look at my pegging practices, do some research, and try out some of the specific techniques that Jay has suggested.
Thanks to all who have been participating on this thread, it has made me rethink my own practice. It's good for young guys like me to see this kind of debate.