a. Mepis, although not running a 3.x kernel, does run a 2.6.36 kernel (as opposed to Debian 6.0's 2.6.32 kernel), so that's something at least.
b. I guess, but for normal desktop use is there really much to gain? These are 'desktop' distros/respins we're talking about here. I run ext4 on my main workstation and am happy.
c. Mepis also has this, it has everything Debian Stable has, possibly more recent versions of other DE's/WM's in their repo... but both PC-BSD and SimplyMEPIS focus on KDE and do a lot of work to integrate it, so that's the comparison that matters in this case, IMO.
d. I don't have enough knowledge of the extent of Debian/Mepis VS FreeBSD/PC-BSD documentation available, so I guess I'll take your word for it.
e. The Debian developers do MASSIVE amounts of work to integrate the fragmented GNU/Linux components into a cohesive whole. My experiences with both Debian and Mepis show that they've done this job very well, albeit always resulting in software versions being a bit dated at the time of release.
All that said, understand, I don't think PC-BSD is "bad". I booted the live DVD and played around with it for a bit and it seemed pretty great, I just struggled to see noteworthy benefits over Mepis, whereas I can find some examples of hardware/peripherals that have Linux driver support, but not BSD support, AMD/ATi proprietary driver for one, Canon printers for another (last I checked).