Tamron 17-50 2.8 versus Sony 16-50 2.8 ?

Anyone actually got both and compared them?

I have the Tammie and my copy is very sharp and contrasty at all apertures - a really great performer. But I have an a77 (body only) on the way and have read good things about the Sony lens, its virtually silent SSM, and its sharpness.

Has anyone ever compared the performance of the two on an SLT ? The Sony is twice the price or more of the Tamron, at leasr, here in the UK.