I recently changed my Sigma 150-500 for a Nikon 300mm with a converter. I was really pleased with the Short-eared Owl photo but other shots have so far been a bit hit and miss. However, when the lens is used without the converter it really is very good and a couple of shots here from the garden shed of the birds coming onto the seeds are a good test. Out in the wild of course the lens is not quite powerful enough but hopefully as I get used to it I will get happier with the combination.
For those that may be interested I now have photos on Flickr with mainly my older stuff working through gradually to my recent photos. You can find these at