Shouldn't come as much of a surprise that WWE saw their overall numbers spiking during the last golden age. SummerSlam 1998 was the most bought SummerSlam in company history, and WrestleMania XIV before it was the most-purchased 'Mania since 1989. That TV rating for Sunday Night Heat indicated huge interest in the Rumble, and the numbers after the fact backed it up.
The 1999 Royal Rumble did 650,000 buys, a record at the time for any Rumble. That's up 48 percent from the previous record holder, which was the 1991 show that did 440,000 buys. No other Rumble had done more than 400,000, though that would certainly change.
As of today, the 1999 show is the second-most bought Rumble in history. It won't take long for these lists to tell you what the current top dog is.