Chicago definitely has the momentum advantage on Wharton right now (actually, they probably have the momentum advantage over every top 20 program). That said, however, changing a perceived brand value of a school is a hard and long process. Given Wharton's huge alumni advantage (something like double the alumni base), it will take a while for Booth to pass up Wharton from a brand perspective.
That said, in 5 years, I expect Booth to make some serious headway on closing the already small gap between the two schools. In this time frame, I don't expect Booth to pass up Wharton, but it wouldn't suprise me if they're considered more equal than they are today (actually, I think they're pretty equal, but enough people claim a huge difference - i expect the numbers preaching the huge difference to decrease in the next 5 years). Even if Booth doesn't catch up entirely to Wharton, I fully expect Booth to have successfully pulled away from Kellogg/MIT/Columbia.
If Chicago can keep up the momentum for a decade, or so, that's when things get interesting, as you'll have enough new alumni to start to make a very profound impact on the brand...