McCullough's hardest fight yet was probably Josh Thomson back in 2002 (yes, over 5 years ago), which he lost by unanimous decision. He also has losses to Harris Sarmiento and Kenneth Alexander. When he wins, the opponents are extraordinarily easy, and he usually defeats them by an easy margin of victory.
However, I do not see his next fight being the breeze that some in the past have been. He will be fighting Jamie Varner at the upcoming WEC 32 event. Varner boasts a 13-2 record, fighting mostly in Rage in the Cage. The reason I don't see McCullough cruising is simply because Varner has matched up against stronger opponents - and he's beat them.
Varner is a stern challenge for Razor, no question. The problem isn't so much that this author neglects to mention the win over Rich Crunkilton. Crunkilton's foolish gameplan cost him a fight I thought he could win. The problem is how much Razor's wrestling is underrated. 5 years in MMA is an eternity and Razor has been working steadily with a team of excellent wrestlers to improve his takedowns and takedown defense. Is it good enough to stop the All-American Varner for 5 rounds? Certainly not. But I've seen footage of Razor avoiding takedowns from wrestlers who hit deep penetration steps or clean duck unders and still couldn't finish the takedown.
The question for me is when Varner is in deep territory and the fight is started on the feet, will he have enough grit to stick to that wrestling gameplan? I'm not so sure. This fight is incredibly difficult to forecast, to say nothing of Razor's KO power that could end the fight at any moment.