MONTREAL — Grudge fights are big business, especially when a superstar is involved. We already knew this. For evidence, we can point to Brock Lesnar vs. Frank Mir highlighting the monstrous UFC 100 or Rashad Evans and Quinton Rampage Jackson drawing over 1 million pay-per-view buys for the culmination of their feud, or going back even further, the Tito Ortiz vs. Ken Shamrock trilogy.Apparently, we can add Georges St-Pierre and Nick Diaz to the list. Shortly after UFC 158 concluded, UFC president Dana White told the media that all indicators pointed towards a buy rate that would equal 2012’s biggest show.It’s trending with Chael Sonnen-Anderson Silva, he said.While the UFC doesn’t publicize its pay-per-view numbers, MMA Fighting’s Dave Meltzer, who has long been considered the foremost expert on such things, reported that Sonnen-Silva II, which took place last July, drew 925,000 pay-per-view buys.That would mean that St-Pierre vs. Diaz would be a big jump over St-Pierre’s return to the octagon last November, when he faced Carlos Condit. That show was still a hit, but did 700,000 buys, putting it firmly into the top three shows of 2012.That could mean that UFC 158 rides its position to the end of the year as the top-drawing show, but the UFC still hopes to produce at least one super fight in 2013 which would likely topple the 1 million mark.UFC 158 was also a success at the box office, drawing 20,145 fans and a $3.71 million gate at the Bell Centre to watch St-Pierre trump Diaz in a unanimous decision.