Joe, what you're asking to see is revealed in the link to the-digital-picture posted earlier. All aspects of lens performance are shown there. You just have to do a bit of work to understand what it is you're looking at, and put it in context. All that information is available on the site.
The portrait test shot that you're asking for would show nothing - zero difference. A test like that is not very demanding in terms of ultimate quality, and neither is it truly repeatable and therefore pretty hard to draw comparisons from (key point for lens test websites).
The two lenses you're talking about - 70-200L 4 IS and 70-200L 2.8L 2.8 Mk2 - are amongst a small number of the very sharpest lenses available anywhere. It needs a very tough test to separate them and further, since the only noticeable difference is corner sharpness, a portrait is unlikely to show that at all.
In practical terms, the upside of the 2.8 Mk2 is that it is one stop faster and can take a 2x extender yet still deliver a very high standard of sharpness and retain AF. The downside is double the weight and price. That's it - everything else, both in terms of optical performance and mechanical function, is so close as makes no odds.
This is pretty remarkable result for the 2.8 Mk2 lens, which you would usually expect to get noticeably beaten by an f/4 design, and IQ start to fall apart with an extender attached. With every other 2.8 version, that's what happens.
Some more pics for you http://www.wlcastleman.com/equip/reviews/aps-c_port/bokeh/135mm/index.htm If you check the size of of the background highlights there, they fit the 1.4x theory quite well.
