If you're dedicated to running straight 110 gas you would get a nice bump in power by going to a 14:1 Piston. If you're staying on pump gas just use a stock Piston with a tighter squish. Who's doing the porting? I'm sure they will have some opinions on the Piston.
09 YFZ450R: 480 Athena, MMAD 14:1, Barkers, Vortex, MMAD +1 TI head, Lightspeed/warpspeed cam, Carrillo Rod, 44mm TB, FCI, Precision Stabilizer, Shcok & Vibe Clamps, Houser Slicast, Fox Evols, Motowoz
06 YFZ450: Venom Port, FCI, Dasa, Venom 12.25:1, 42mm FCR, Cam Mod, NCVQ Needle, CCP Stabilizer, LSR DC4, Elka Stage 4's, Shock & Vibe clamps