echo, my first marker was an Ion and I recently upgraded to a PM5. Having held a PM6, the weight and size difference is noticeable but I see no reason to upgrade at the moment. The PM5 I have has a couple of required upgrades, name an OOPS and feedneck, along with a barrel and trigger.
The internals of a PM6 are almost identical to that of a PM5 and the PM7 is again similiar, but with extra modes built into the stock board. As I play division 4 NSPL, I have no need for modes other than semi but have recently bought a cheap Millennium board should I want the capability of ramping.
It is quite a large and heavy gun in comparison to the more recent releases, but if you can cope with that then you might as well spend more money playing than on a new marker.
-Will