hrm, the last time I checked 40 size fliers are park fliers =) so it will work fine for those and for most other aircraft of that size, of course except competition performance aircraft where lantency is very important.

quote from page 2 on the dx6 manual
"The DX6 system is designed for parkflyer type aircraft only. This includes all forms of compact electric and
non-powered airplanes as well as micro electric helicopters. While the system has more than adequate range for
these types of aircraft, it is imperative that the system not be used in larger aircraft that could exceed the range."
http://www.spektrumrc.com/ProdInfo/Files/DX6_Maunal.pdf

If the mfg says that it is not a full range radio... then unfortunately it's not a full range radio, although it will work for many aircraft out there.

again though, the main question was what is the difference between the dx6 and the dx7, not if the dx6 had plenty of rnage for a 40 sized flier, which it obviously does =)

I'm not trying to be confrontational, but hopefully that makes sense.