Er... firstly i think the 55-300 is cheaper than 490

anyway, i did a one to one comparison of the 70-300 to 55-300... not at 100% though, but i cannot really tell the differences... perhaps u should see one urself, if u urself cannot see the differences, then i think it does not justify the increase in cost to get the more expensive one.
the 80-400 i have use it for a while, it is heavier, a lot more costly. It is not a AFS, so AF will be slower and of course noisier, and if it cannot AF under low light, it will hunt, thats where the noise will be louder, however the image quality is good. But if u do buy this lens, pls check throughly, i have seen some sharper copy while some softer.