It occurs to me that Chatham Center is sitting right there and available for use as a model. Something along those lines in terms of height and density (but not including the anti-urban plaza), and allowing for the low-rise corridor right along Wylie, would be a reasonable target for the blocks nearest Downtown, and create a pretty coherent step-down from Grant:
http://binged.it/ICRa1e
Incidentally, I agree that a more organic approach might be a good idea. I certainly wouldn't mind if the Penguins wanted to start on the upper/eastern end, because I think the case for higher-density use in the lower/western end is only going to improve with time. However, if a major tenant wanted to step up and fund something cool in the nearer future, that would be OK with me too.