Thanks for the words of encouragement Bob, I appreciate it. I've never watched any of the world's top casters in action (besides Mel Krieger and Geo. Roberts on video), so only know how to cast from being on the water with others, practicing, and reading up on the subject... it will be a long, long time before I think I reach anything near expert status.
As I had said previously, my casting stroke is waaay off-vertical, nearly to the point of side-arming. When I cast in this fashion, the loop in the line during the forward and back casts is very tight, and this is undoubtedly why I can attain relatively good distance with consistency. When I bring the cast up to nearly vertical (i.e. probably within 15 degrees of vertical), my loops are never as tight and I don't get the same distance as a result. This applies whether I'm double-haulinga, water-hauling, etc.
Now, I will say that I've always been able to throw footballs and baseballs farther and faster when going "side-arm", more than likely because my personal range of motion is better in that range of plane. I realize that throwing a ball may not be synonymous with casting (particularly from what Roberts has to say), but the point I'm trying to make is that I imagine that this "side-arming tendency" has some significant bearing on my casting stroke, and I would also imagine that each person has their own "comfort zone" that they will cast the most effectively within. Also, rod action probably enters into the equation to some extent.