After following this thread for some time, I decided to buy Tamron 70-300mm VC lens as an upgrade for my canon 55-250mm IS lens.
I did compare both lens and VC on 70-300mm is way better than IS on 55-250mm.
Posting few pics taken with new lens, all Cropped and edited.
Western Scrub Jay by Madhvesh Joshi, on Flickr
IMG_7365 by Madhvesh Joshi, on Flickr
IMG_7336 by Madhvesh Joshi, on Flickr
I think this lens is an under rated lens. If focuses fast and the VC works very well.