I'm no expert, but I've always thought the difference between the 707 and the 7070 was the date it was made; the 707 would be an older bow. As evidence, I own two 35# Colts, a 707 and a 7070. On the 707, the riser wood seems to have nicer grain, and the logo on the limb has a picture of a colt. The 7070 logo is only the arrow through the Ben Pearson lettering. Either way, both bows shoot beautifully. I've noticed this same trend with the Hunter as well, models 709 and 7090; I'll do some more research.
Guess I'm a bit of a Pearson recurve nut, because I just bought a 55# Colt (7070) as well. Got it last week, did a basic set up that night, and sent about 2 dozen arrows accross the shelf. Smooth draw out to my 31" draw length, quiet shot with no hand shock, and a FAST shooter. Love the old Pearsons!