Cropping won't do anything to the bokkeh (apart from draw attention to it) - heavy PP can mess it up, in particular local contrast enhancements like the LR Vibrance slider, but that's really wiry... I'm not a fan of the beercan - I had 2 and sold them both. Great value for under 100quid (well, it used to be), but equally, performance only a little in excess of a lens that costs less than 100quid. The beercan's bokkeh is prone to exactly the same type of specular highlighting I'm seeing from your 70-300 - it's just that most people eulogise it and that it's built up a huge rep.