I have had both radios. The M11 is packed with more features than most racers can use and I did like the backlight feature as it makes it a bit easier to read.
The DX3R is lighter and is to me the easiest highend radio to program. Don't get any easier to use than this radio IMO.
For me I swithched from the M11 to the DX3R and ran faster lap times for whatever reason. Only change was the DX3R receiver as I used the same servo, speedo, motor combo, and car setup but was continually faster with the DX3R as it felt like the car steered better and accelerated faster.
The laptimes showed I was up to 3 tenths faster a lap. Could be the DX3R just felt better for me so I might of pushed harder but not 100% sure on the reason but thats what happened for me.
The DX3R has one advantage that I can see is you can use any Spektrum receiver with it while the M11 has to use the Airtronics 4 channel 2.4 receiver. You are limited to this one receiver only. If you already have Spektrum you can use you older receivers.