I love my M3. Is the M3 you're looking at a preban (PG + mag extension)? I've seen those go for upwards of 1k so I'd consider anything around there or lower a good deal (of course, that's just my experience/observation). If it has PG but no mag extension, I've seen those new for $700. In semi-mode, it feels like an M1. I love the pump mode also. It's just different and seeing that you already have an M1, you're probably looking for something different too.
MrJones