Basicaly,...which one is the smallest model?, usually the MSX2 and higher models are bigger (NMS8235! 
); s I guess the smallest will be a MSX1...
Edit:
...and the OCM doesn't counts...
MSX dimensions
It's Not the Size that Matters, it's how you use it 
I guess the CASIO PV7 is the smallest MSX around... But other CASIOs are also very small.
you're right... Casio PV7: 307 x 210 x 33 mm / 1560g
Wow!, smaller than a centrino mobile! 
...but, hey!, the Casio PV-7 it's the only one MSX with 8Kb RAM, that's why it weights so little...
Well, then which is the biggest one?
Maybe some pictures of the smallest & largest machines here. For comparing.
Without separate keyboard, my vote goes to the Philips NMS8235
Now we need to scale the images...
About docking stations, as the one shown in the above picture of the CASIO PV7, are there others for MSX computers? CASIO has several of them, but did other manufacturers create docking stations for specific MSX models?
SVI produced docking stations too, but for the SVI 8XX series (non-MSX).
About the biggest MSX, I don't know. But regarding the most heavier, I'm pretty sure that the winner is the good'n'old SONY HB-700! Metal casing rulez