Cool, so I can spend £1147 on the Canon combo with 2 stop OS or £695 on the Sigma with four stop OS and get pretty much the same results ... and with auton-focus
I too want the 150-500 OS to be optically good, as it presents a tantalizing alternative to the 100-400 for a compact wildlife lens with stabilization.
Our local Sigma distributor here has made available to me a review copy of the 150-500, and I went to their shop to pick it up several weeks ago. That copy was very soft though, so I'm waiting for their next shipment so I can pick the best of the lot. A couple of birding buddies have bought theirs, and I've handled one in the field. OS and AF speed look decent, but again the optics don't impress.
I've not given up yet on the design, and I'm hoping that optical issues (I always use MF via Live View in checking IQ to preclude any AF issues) might just be due to early production run hiccups. Perhaps in a couple more months, we'll be able to see the full potential of the 150-500 design, as more copies (hopefully some are good ones) reach the hand of experienced shooters.