I don't know; I just went through the entire catalogue ripping all my Maiden to hard drive, and collating the b-sides and what not... and I don't think it's really a fair comparison. They're very different drummers. While Clive helped light the torch, they did things after that they never would have been able to do with him. Nicko is technically a superior drummer. I know in one of the docs (The Early Days or 12 Wasted Years; there is some overlap) Bruce makes a comment to the effect that Clive was his "favorite" drummer, but he says it in a way that is more respectful than really an objective criticism (or a dig at Nicko). Killers is one of, if not my favorite, Maiden records, so there's no beef there, and certainly, he was integral to the fire that was the Number... album cycle, but they elevated to the next level with Nicko.