Damian,
I guess I'll just say that for starters, I'm no expert on the subject. But here is my opinion on the charts.
For sure, ISO charts are a big part of it.. but not really the only thing that makes a lens IMO. Take the 50mm f/1.2 for example.. While Bryan does say that it has " the best image quality they (you) can get from f/1.2 to f/2", he also talks about how sharpness isn't everything, speaking about the color and contrast and flare control. The ISO charts make this lens look sloppy like a pig stopped down, even compared to the nifty fifty. (I guess that lens could be another example, super sharp but not always a desirable real world result.) But when I go through the flickr group photos for the 1.2, I just don't see it. I see amazing images.. and the lens is on my wish list.
Me, I read his reviews first, then I take a look at the charts if I'm really curious.. but I rarely put a ton of weight behind my decision based on that alone.
I guess ISO charts are helpful, but you still have to consider contrast, color, aperture, IS, build quality. For some ISO is a big piece of the puzzle though.