I own an Empyre, my father-in law has the CB6048, a friend has a NC, not sure what model number. You'd think I'd be biased, but I'm not. I have done boat loads of research like it sounds like you have, and from what I've seen and read, the Portage and Main is by far the best Wood boiler out there. I drove down to Louisville Ky. about 5 weeks ago and looked at every manufacturer there, and the Portage and Main guys were the only ones who gave realistic efficiency ratings for their units. Some of the manufacturers actually want you to believe that their boilers will get more than 90% thermal efficiencies out of their gasifiers and as high as 75% out of their non-gasifier units. (one dealer actually told me that theirs tested at 107% at the EPA test site) Anyone on this site can tell you that that is simply not possible unless you started with wood that is at 0% moisture. Brian with Portage and Main(I don't know what position he holds with the company) gave me and everyone else that was in attendance realistic expectations of what today's modern boilers can achieve. As far as efficiencies are concerned, there isn't squat for difference between any of the top 5 or 6 players, so to me an investment like this has to boil(pun intended) down to construction and manufacturer support. The Portage and Mains are easy to work on if you have to, and the way they are welded together is better than any that I've come across. At the end of this burning season I am going to get rid of my Pro 100 and drive more than 100 miles to buy a Portage and Main. That's if spring ever gets here!
That's my 5 cents.
P.S. Anyone interested in a 6 month old Empyre Pro Series 100?
Marty