Based upon what the bell system guys were doing 50 years ago, it seems that 45Mbps over a 70-100km radio link appears it ought to be doable.... but really, 10Mbps over 50km would be a good start.
We don't all have mountaintop microwave sites....
We have homes and ham stations in compromise locations with city lots, restricted antennas and big RF absorbing trees... 25W of 440 MHz will probably get through where less power at higher frequencies won't. The UDR56K is a good compromise real world solution that is probably the last best hope for AMPR data... The speed is good enough for IM, email like this list, megabyte files (I know first hand that's possible...) and facebook clones. That's way more than what we have now... The price per node (about $600) is high and will be hard for many to justify but it beats the competitors - ID1 is $1+K for 120K raw data with 10W at 1.2 G or D710 with 50W of 9k6 data UHF or VHF for $700.
Let's raise the bar a bit and get to building a RADIO BASED NETWORK!
A harder problem than the RF is the WHY.... I can download Zombie videos at 40MB (or ? - I haven't checked lately) from anywhere in the world - why should I futz around with silly HAM regulations and bureaucracy to do limited Ampr data... (FWIW I know the answers to that...)
Eric AF6EP
73 Bill, WA7NWP