The major differences between the 6.0 and 7.3 are the newer engine has four valves per cylinder, a variable rate turbo for faster spool up, a five speed automatic transmission, and is supposedly more emissions compliant than the 7.3L. That said, I have a 7.3L that I have kept. Last year I put the Banks Power Pack System with Power Elbow and Big Hoss module in my 7.3L. I have driven all the new trucks from each manufacturer mentioned and none have come close to the performance of the 7.3L I already own. I have monstrous power, and can get about 22 mpg highway and 15 city and 14-15 pulling an 8,000-9,000 pound load on the freeway. Of course, as advancements continue, the new engines will make progressively more power, but for now, the 7.3L I have runs really well. It is paid for, and I drive to dealers looking but always leave with my truck. According to the guys at Banks last year, the ones that work there that drive Fords, still keep their 7.3's. Of course, they are coming out with products for the 6.0L every day.
John M