Interestingly, the 1991 WFT and the 2000 Ravens both shut out 3 opponents in the first 5 games, not just 2 in the first 4.
WFT defeated Detroit (45-0), Phoenix (34-0), and Philly (23-0). Detroit finished 12-4 that year and Philly finished 10-6, so pretty good teams. Phoenix finished 4-12.
The Ravens defeated Pittsburgh (16-0), Cincinnati (37-0), and Cleveland (12-0). Pittsburgh was the only one who finished with a winning record at 9-7. Both Cincinnati (4-12) and Cleveland (3-13) were in the basement. FWIW, Baltimore didn't even finish 1st in their division that year; they were the #4 seed at 12-4.