being a birder on budget, i'm always on a look-out for "bang-for-the-buck" equipment

after reading all the +ve reviews on this lens, i rented it for a day to test it before seriously thinking of buying it.
my initial outing with it was a "disaster" as the scene i was shooting was very challenging for most camera's focusing system. then i tested in on "more friendly" feathered friends in my neighbourhood and this lens proved to be very capable up to 550mm, stop down to f8.
my current setup is EF400f5.6 + kenko 1.4TC which can AF on 70D, both OVF and LV. It AF very well in LV mode on the 70D because of the dual-pixel sensor AF. so, my layman assessment will be at 560mm, how well can the tammy perform. AF is decently quick, definitely quicker than my current setup. But it does hunt under low-light / shady environment (eg. under leaves or under shade). So, in this aspect, the tammy met my requirement.
now, the image quality. i guess, a picture is worth a thousand words.
here are some test shots to share~
cute sparrow

552mm, f6.3, iso1600, 1/400s, tripod
olive-backed sunbird

552mm, f8, iso800, 1/200s, tripod
brown-throated sunbird

552mm, f8, iso400, 1/200s, tripod
pink-necked green pigeon

600mm, f8, iso1600, 1/640, handheld, vc on
no sharpening done on all the shots.
my user conclusion is this lens is very capable up to 550mm and is able produce very good quality images. it will not be able to produce what the big guns can produce in terms of details but for the price tag it has on it, this will be one of the "bang-for-the-buck" stuff. tough decision for me now... haha...
check out the other shots
http://www.flickr.com/photos/koobird/sets/72157641290350854/with/12667377373/
cheers & take care!
david