Brian,
You are correct - it is more pixels on target.
A couple things: if you plan on ceiling mounting these and looking down a corridor, you need the 2MP, the 1MP doesn't have enough tilt to see that far down the hallway (unless you have very high ceilings - which will in turn hurt your PPF). It is a design flaw IMHO. (Note: they both have the same tilt, it's just that the 2MP's wider view compensates for the limited tilt).
The lens option Ethan recommends should work great - but it MAY ruin ceiling mounting for BOTH cameras. (I haven't tried the longer lens - but unless it somehow allows for greater tilt - your going to be in trouble).
Now, before you go and decide you are just going to wall mount it, understand you will need to mount to a wall at the end of the hallway (or a soffit that runs across the hall). This is again related to the limited motion of the camera gimbal. See my diagram below.
This set of issues drives me nuts! We do LOTS of long hallways that would be perfectly suited to these cameras if it weren't for these issues.
That said you CAN force the M3004 past the tilt stop point in a pinch. We did it on 2 cameras when we first discovered the issue. It makes a horrendous sound and likely voids your warranty. Also, it will likely not be possible to force it past the tilt stop point once you have installed the optional longer lens.
The Acti D61/D62 cameras should cost about the same or less than those being considered (with considerably larger sensors and better lenses to boot). Be warned; It seems Acti has some issues with their VBR codec (at least as it relates to Exacq integration). Also - I don't know if Acti can do corridor mode (is Axis the only mfg that does corridor mode? It is just a 90 or 270 degree rotation of the video). Loosing corridor mode would be a big bummer, as it eliminates a lot of wasted pixels on the wall, and (more importantly IMHO) a bunch of dead space below the camera.
I haven't used the Acti products yet, but we are seriously considering them.