If it were me, I'd go with the 657 all the way, as long as you're not going to be gnar-ing too much shred.
I'd also put in a shout for a 1997 - 2000 Marin FRS (Mount Vision, Rift Zone, East Peak etc etc) if the 657 doesn't work out. I love mine, and they're very versatile bikes.
Myself I have an urge to build up a GT RTS, ideally one of the purple ones...