I've just checked out the Trek specs, the 820 is made from hi tensile steel with one tube of chromoly. Hi ten is the lowest grade of bike steel and not what you want on a tourable bike. An upgrade to a full cromoly frame would be a big advantage.

If you want to hang your butt out more, then it could be either:
You are using cranks that are too small. If your 3:00 crank position moves forward 1cm, then your butt will follow.
Your seatpost does not have enough layback. In the old days before a wide choice of laybacks, builders had to vary the seat-tube angle to position the rider but these days most people should be able to get a good position using choice of seatpost.
A larger frame will not neccesarily cure the saddle position. The seat angle may be 0.5 degrees slacker but that does not amount to much. If your seatpost is at the max and you still need more extension, then yes you do need a larger frame.