The australorps I have had have been much larger than any of my other birds. Since JGs are bigger than australorps (as far as I remember), I would imagine you would definitely get a decent sized bird from that cross.
I might have a couple of these in the incubator. I'm not sure why, but I tossed in 6 eggs. Some are BA eggs, and I only have 2 roos, one of them being a JG. They really look pretty similar anyway, so I guess we'll see. If they hatch, I'll put up some pics.