Sharper at 500mm?

First notable image taken at 500mm with the Tamron 150-600mm. Reviews I've seen claim the Tamron is sharper at 500mm than 600mm. Hard to tell, because the lighting was really good, allowing me to step up to f/10 and be at ISO 500. Time will tell where this lens will best perform.

Chipping Sparrow Nikon D7000 ISO 500 500mm f/10 1/640 sec.