The 91XG is a UHF-only antenna. The 8200 is an all-channel antenna. That's why it's 10 feet wide at the back and 14 feet long. The UHF portion is the front part, the part that resembles the 91XG. There's nothing on his TVFool chart that suggests an all-channel would be either necessary or even useful.
For UHF only the 91XG is superior to the UHF section of the 8200. However, channel 7-13 still need coverage for his major stations. If you want a single antenna, the 7698 would be the equivalent to the 8200 without the big, honkin' channel 2-6 elements. It would easier to try the configuration already suggested unless you want to try to handle a behemoth like the 7698.