If Pedro, Peavy, and Oswalt are still around, does that mean Sheets or Perez is too? If all those guys are there and you are on the short end of a snake draft, try to project whether any of the latter 4 will still be there on the return; if so, go for hitting now, get one of the 4 on the back end. The cafe could argue endlessly over who's the best of these 4, but in the end it just underscores that there's little diff between 'em and if you can grab one in a later round, so much the better.
If you're on the long end of a snake draft, you'd better take one now - otherwise you might be looking at no stud SPs through 6 rounds, and you'll have to get mighty lucky in the latter rounds to atone for it.
just my .02
Edited to add: Good post, DK. I basically ignore advice from anyone who consistently posts without reading thru the thread. How do I know they put thought into mine?