I disagree. I can tell a pretty significant difference between the 60 and 85 at higher speeds. I've noticed this with loaners I've received. It's like the 60 just runs out of juice while the 85 keeps pulling through.
I actually got a P85D loaner today and at low speeds, it is crazy faster than my 85, but for normal highway passing (really anything about 45 - 50 mph), I don't really feel much of a difference between the P85D and my S85. If anything it makes me feel better about not having a P85D. Now, that 0-60 is just INSANE!
There is no difference between the 60 and 85 running gear with the exception of the battery.