It's simple, Ben Sheets is a better pitcher than Oliver Perez.  He has command and nasty breaking stuff, unfortunately there is one huge risk factor...he can't stay healthy.  This is why Sheets isn't commanding 75 million over 5 years.  If he pitched over 200 innings, even just 2 of his last 5 years in the majors, he would be a golden goose. 

Oliver Perez is an intriguing character,  he's fiery and sometimes he looks unstoppable, but other times he looks like Wild Thing (before he got his glasses) in the movie Major League.  If Omar is considering going past his 3 year/30 mill deal that was already proposed, then Scott Boras is officially the anti-christ...how else could we explain the deception and the front office mind control.  I haven't even heard of another team making an offer to Perez, so why would Omar improve his.  It should be simple economics, amounting to supply and demand, if Perez is not in demand then why supply him with additional money.  When a product isn't selling well at Walmart, they don't raise the price and hope it does better, the price is reduced.

Omar, take note: Sign Ben Sheets to 2 years / 16 million guaranteed + 8 million in incentives.

After that, go get Orlando Hudson and take a page out of the Dodger's book and cut ties with Castillo like they cut ties with Andruw Jones.