"That Nikon Guy" on youtube has part of what you want, a Canon 24-70 L vs Tamron 24-70 VC comparison. Very in depth.
... though one doesn't necessarily has to agree with nikonguy's conclusion, nice videos, but he's very amateurish, I agre with Albi86 on that. Don't miss his bonus video "how to shoot a model" :-)
Esp. him saying that the vc is great for handheld video - I could not second to that, because while the frame is more stable, it jumps around like with any IS, no substitute for stabilization gear. And he only tries very few "walk in the park" situations, so every potential Tamron buyer has to figure out how much the "onion" bokeh concerns his/her shots.