Well, that's the question I've been asking from the beginning. The 550 is so sweet, why do we need the 543? And it's not just the 550, cause the 545 has more power than the 543 and costs less. There are times that a 242XP is just the perfect saw to run, and I'm glad I've got a couple. So, if the 543 can keep up with a 242, then there is a market for it. I sharpened up my 242's last night in anticipation of the upcoming grudge match.
(My money's on the 242)
But back when the 242 was on the market, the next step up was the 254, and the difference in weight between the 2 was more significant than comparing the 550 and 543. Sort of like the MS241 and MS261 today.
From the 2014 catalog, here are the specs. (I must be feeling Norwegian this morning lol)
543- 2.95hp; 9.9 lbs.
545-3.3hp; 10.8 lbs.
550-3.7lbs; 10.8 lbs.
445- 2.8hp; 11.2 lbs.
Compared to the 445, it looks real good. About the same power, but nice and light. Compared to the 550, or even the 545, I think you give up too much power for a smaller savings in weight.
I think it's going to come down to what are you actually going to use it for. A light saw for climbing, bucket work and other limbing tasks. For that it makes sense. If you want to cut firewood with it, then the 545 is a far better choice.
I'm also anxious to tach this saw, as I've heard conflicting reports about what RPM's they are going to run at. 15,000? 16,000?