Here's a quick video showing the autofocus speed of the Sony A7 and the LA-EA4 lens adapter. The LA-EA4 allows the Sony Alpha / Minolta A mount lenses to be used on the Sony A7 with phase detect autofocus.
Sony A7, Sigma 50mm via LA-EA4 Adapter
Here is Mr. Ticknor giving his impressions on using the Sony A7 with a Tamron 70-200 f/2.8 lens via the LA-EA4 lens adapter.
Sony A7 with Tamron 70-200 f/2.8 Impressions by Ticknor Photography