540xp is 3.9kg and 1.8kwNo 545/550 are both in the 5,5kg area which makes them all-round saws not lightweight delimbing saws.
135 weighs something like 4,7 kg so for a light limbing saw that's getting a bit heavy..
I would look at a 435 instead since they only weigh 4,2 kg.
The lightest pro model is the 543 at 4,5 kg.
Really the best light delimbing saws is going to be battery saws from now on...
550xp is 5.3kg and 3.0kw
135 is 4.7kg and 1.6kw so worst of both worlds.
435 is 4.2kg and 1.6kw so marginally better as you say. Pro saws still miles better, and much better made.
Depends if they mean delimbing up a tree or on the ground. Up a tree I would choose a t540xp, though I used to use a 435 because I was being tight, and I would not recommend it, they are very slow compared to a 540xp or ms200. On the ground I use a 560xp, but a 550xp would suffice.