Yeah, that's what I'm thinking. I'm in the same boat as you - 12 yo frame (a Dean). Dunno what it was originally designed for, but I would guess less than 80mm. The SID does look like it lets the wheel suck up a bit more vs. my Manitou 4. It's only an inch longer at most fully extended, but certainly has more than 1 inch more travel. The lower tubes of the SID are shorter than the M4.
Laziness is also playing a part - you basically have to totally disassemble the fork to convert it and I don't really feel like doing that with a brand-new fork. I here the SID needs rebuilding a lot so maybe I'll plan to switch it to 63mm at the first rebuild. If I don't absolutely love the extra travel, that is!