My longest tour so far was eight weeks, 2500 miles. The bike was a heavy expedition tourer weighing in at 36lbs. I started with 40 lbs of gear, but mailed between 5 and 10lbs home after a couple of weeks, when it became clear I had more than I needed. I weigh around 200 lbs (should be lighter) so even at the heaviest my bike plus baggage came in at way less than half my weight.
My view is that the length of trip is almost irrelevant. Once you have enough gear to be self-sufficient for a week, you have enough for three months. However long the trip I couldn't see me loading up with more than 30lbs these days.