From an older post.... same basic information.
Buying a Tamron Sigma 70-300 type of lens, you may well throw out a lot of images when you get the same critters with better glass. Mine ended up being a waste beyond establishing that I'd like to use longer glass. But once that was done, I wish I'd bought something better a lot sooner.
K-5 and Sigma 70-300..
K-3 and DA 55-300 PLM
There is absolutely no comparison, based on my copies of these lenses. This image taken a few days ago (May 18). I had my choice of the DA*60-250, DA* 200, Tamron 300 2.8, F 70-210, in good light, the DA 55-300 is right up there with them. I do leave it home on over cast days or in low light situations.
Even with the HD DA 1.4 TC on mine produces acceptable images, as long as you have enough light.
The best thing about the DA 55-300 PLM, when you do decide if you do, you won't be throwing out your images when you get a faster lens. Any image you get will stand up, no matter what else you get. Your problem will come from when you don't have a fast enough aperture to actually get the image in the first place.
I even use it (carefully to avoid vignetting) on my K-1.
it
K-1 and Tamron 300 2.8 with Tamron 2x TC
For when you get serious.
Or Tamron 300 2.8 and 1.7x AF adapter on my K-3
Even though I'm still using the image, the Sigma 70-300 just didn't meet minimum standards.