I don't really pay attention to my average MPH, but I know that I'm always pretty worthless the first two or three days of a fully-loaded tour. The miles feel endless, my body feels worn out, etc. After about the third day I start to hit my stride. Before long, 70 mile days aren't bad at all. I've begun big tours in various degrees of being in shape. Before a four week tour down the coast, I had a hernia repair. I wasn't able to train until two weeks before my ride left. The first three days were awful. I had planned a short (10-15 mile) ride on the fourth day, then a rest, but after I got on the bike that fourth day, my aches and pains had left and I felt great! I rode 40 or 50 miles that day. Before another long tour I was able to train for months. I felt like I was in pretty good shape, although my training was without luggage. When the tour started, again, I was pretty wimpy. But this time it only lasted two days. On the third day I was feeling strong.

Now I try to make my first day really short - 25-30 miles, my second day not much longer, and don't really plan on covering much distance until the third day. I think it's good to be flexible. If you feel wimpy, don't push yourself. Take it easy until you feel like riding further. Eventually you will.