Likewise, I got some cracking shots with mine - and geoffrey Crawley and AP tested all of the superzooms and found this the best. Caveat - 'for the price', but we all knew that already. If money wan't a problem, we'd all have 600mm f/4's, and that'd be that.
Having said that, there was some question over its overall sharpness when I recently put mine up for sale; I withdrew it from sale and presently it's getting the once-over at Tamron UK, ready for sale again once it's CLA'd. [Mine was Nikon mount, so of no interest to you]. BTW, £400 is a great price for this - Mifsuds had one sell recently for £570, and new they're nearer £850.
It may well be that 100% crops aren't what this lens is about. Still, if you want true optical 500mm for the money, no zoom is going to be perfectly prime-sharp at 500mm. Again, no surprises there, or we'd all have Tamron zooms and there'd be no 600mm primes.