m43 @ an equivalent of 600mm can give nice moon shots, better than cropped full-frame photos. That also goes for some birding shots I saw here. Gomen...If you need reach either you better be prepared to carry more kg and to fork out more money for the best quality in full-frame or you use a smaller sensor for that job. Cropping full-frame shots into the nirvana doesn't look that amazing...
Alternatively, anyone interested in birding could take a much shorter lens, even a P&S camera, to a bird park or any place birds are tethered and wouldn't have to worry about cropping. Gomen

Animals in a non-captive environment don't pose like people do; most times a critter photographer has to take what he can get and make the best of it. That's what makes cameras like the A7 and NEX-7 such valuable tools. They produce RAW files that can be cropped heavily if it makes a difference between getting a shot and not getting a shot.
Those of us who aren't too chicken-$hit to post our own photos in a picture-post thread probably aren't using those pics to try to sell to stock. Nor are we seeking the idle musings of a self-designated arbiter of taste/quality. Rather, we're sharing our experiences with the capabilities of the gear we're using, ostensibly in a constructive manner.