Below is a plot from Channel Master of the CM-4251 measured gain and 91XG modeling results. A pair of stock 91XGs or a 91XG modified with holl_ands extended directors are 0-2 dB less gain than the CM-4251 across the repack band. A pair of modified 91XGs are better than a CM-4251. Based on modeling results, I think it's hard to justify putting up a CM-4251.But that CM-4251 is probably the best long range fringe antenna, although it may be a bit problematic to install due to size and weight.
There's a rule of thumb that I recall from amateur radio that says the time to switch from stacked yagis to a dish is when the desired gain requires a dish 5 wavelengths in diameter. For UHF TV at 470 MHz that's a 10' dish. A 7' dish isn't quite there.