Upgrade From 6500 to New Radios?

I upgraded from a 6500 to a 6600M. The controls and the ability to connect a monitor were the big pluses for me, but that came from the "M" part of the change. As for the radios, It is nice to be able to use two antennas at the same time. I haven't noticed the advantage that contest-level filtering supplies since it was excellent in the 6500 already. The two transverter ports and two receive antenna inputs are nice, however, you sacrifice the receive antenna loop that the 6500 has. I don't detect any significant performance differences between the two. One advantage of the 6600 and 6400 models over the earlier models is the availability of parts for repairs if problems occur.