The bandwidth to the orbiters is up to 2 Mbps, but because they're in low orbit they're only in sight 8 minutes per day.
http://mars.jpl.nasa.gov/msl/mission/communicationwithearth/...
http://mars.jpl.nasa.gov/msl/mission/communicationwithearth/...
What you'd need is a whole series of them to increase coverage.
It is Curiosity that is not in sight of the Orbiters, again because of their low orbit.