I like Timberpig`s assessment of echo quality vs that of Stihl or Husky pro saws. I agree with him.
I also believe the 280 is somewhat of a crossover saw for Stihl, not quite pro, not quite homeowner. I`d put it`s construction quality on par with the Echo, which BTW I believe, shares the horizontally split crankcase with the 280. One of the more distinguishing/telling features regarding whether or not a saw is considered a pro saw.
I have to admit that I`ve never run a CS520 although I did get to run rahtreelimbs CS510. Frankly I was impressed by how that saw revs and consequently cut quite well. I would assume that the 520 is similar, but this is only an assumption.
I have owned a 280 and used it enough to get a good feel for it. It`s a pretty nice saw. Fairly light and well balanced, good antivibe( if a little too soft), better than average air filter precleaning and a decent size flocked filter, and side chain adjust. Oh yeah, also has a fully adjustable carb.
The CS510 felt buzzier in my hands than the 280 but not much different than the 260. It was no match for speed or power when compared to the 260 or 280.
I don`t know what sort of air filter the 520 has but I`ve seen quite a few Echos that have the less restrictive(read: less effective) nylon filters and Echo also seems to be leaning heavily toward non adjustable fixed jet carbs based on the several that I`ve looked at over the last few years. Any echo dealers care to comment on my casual observation?
This is what I`ve found when comparing an ms260 to an ms280. In small wood less than 8" diameter the 260 would come out ahead after 10 minutes of successive cuts. If the would were 12" or larger, the 280 would be the production leader after 10 minutes. The additional pound or so that the 280 weighs over the 260 doesn`t seem to be noteworthy, they are both reasonably light saws, as is the CS520.
What is the better saw if comparing the 520 and 280? That`s very subjective. I don`t think that you would ever be sorry for buying the 280 if the budget allows it, but it is substantially more expensive than the 520. The 520 can be considered a steal at some of the prices I`ve seen them go for on eBay. You shouldn`t have any trouble getting your money`s worth out of either saw.
If you only need a 24" bar occassionally, do you really need one at all? Try working around the cut with the 20, you should be able to cut close to 40" without even cutting any ears. None of these saws will do well with a 24.
Russ