I've never had a 40th or an 80th, just too expensive for me to justify the purchase although I've been tempted just to try them.
You didn't ask
, but I do prefer the 26th over the PAM64 series. To me the PAM is just like a deeper, richer version of the x000 (M) series so it all comes down to value: I have a good supply of the x000, so I don't typically pick up a PAM at the B&M. The 26th is a very different smoke--flavorful, complex, well balanced and perfectly constructed.