"For the mass of 1 MTO, I believe you can build several smaller satellites that would have a higher net capability."

Consider the capacity of Mars Odyssey ( 128kbps ) and MRO ( 4,000 kbps ) -

Mars Odyssey = 725 kg at launch
MRO = 2180 kg at launch

So - for the mass of one MRO - you could build three Mars Ody. - netting you a total of 384 kbps back to earth - an order of magnitude lower than that of MRO

Lets go nuts - lets say you could build 20 100kg orbiters which could match Odysseys downlink capacity (which would be frankly impossible given current technology - or even technology of '09 ) - you'd still be netting just over half the downlink capacity of MRO for the same weight.

And MRO's a science orbiter - not even a dedicated relay asset.

The ballgame changes however - when you start thinking optical back to earth - I'm not sure of the implications of having multiple laser transmitters from mars back to earth - what scope there is for interference on reception, and if different wavelengths would fix that - but - given Ka / X band technology - one big badass orbiter is always going to give you a better downlink capacity than an equiv. mass of smaller orbiters.

Doug