How low could Sonnanstine's ERA go next year? Along with a new approach to facing his big league peers potentially a lot. Statistically James Shields' 2006 and Sonny's 2007 seasons with the Rays were nearly mirror images extending beyond the surface the numbers are even more similar than originally assumed:
Sonnanstine 07: .333 BABIP 40% GB 7% HR/AIR 4.33 FIP
Shields 06: .338 BABIP 45% GB 8% HR/AIR 4.44 FIP
Shields ERA of course dropped 0.99ths of a point, how? Luck.
Shields 07: .286 BABIP 46% GB 8% hr/air 3.94 FIP
Other than his BABIP dropping everything else remained the same, except for his BB/PA and K/PA numbers, both changed for the better, lowering his 7% walks to 4.1 and upping 19.3 strikeouts to 21.1%. Sonnanstine's were 4.7 and 17.5, there's no reason to not believe he can't lower the walks even more and increase the strikeouts.
If the Rays add a defensive shortstop, and honestly there's no reason they shouldn't, his BABIP could drop considerably with the moderate groundball numbers. I usually don't make such fine predictions about team-orientated stats like ERA, but I'm willing to bet that Sonnanstine's ERA will drop lower than one full point.