Much has been made about the underwhelming quartet of pitchers slotted behind Johan Santana to start the season in the Mets’ rotation. And given the choice of Mike Pelfrey, John Maine, Oliver Perez, and Jon Niese, it’s easy to see why the majority of Met fans are pinning their hopes of finding a reliable number two starter on the power sinker of Pelfrey. The tall right-hander has the combination of pedigree, stuff, and age that can’t quite be claimed by the other three. Pelfrey has even flashed enough Major League success (3.72 ERA in 2008) to reinforce such high expectations. But even so, Pelfrey’s stats have yet to jive with his potential, and pundits have questioned his ability to succeed with his current repertoire. And now, this spring, we’ve been hearing stories about Pelfrey’s efforts to bolster that arsenal by adding a split-fingered fastball.