i wouldnt go shorter than 15/43. the thing is with 15/46, your going to be changing gears alot more often to keep yourself in the meat of the powerband and changing gears more often slows your lap times down a lot. a quickshifter is good for shaving a second or 2 a lap depending on the track, which shows how gear changes slow you down.
you also need to take into account the amount of chain links you need for a certain sprocket ratio.
2004 Hayden SP2: Ohlins Shock, Racetek Fork Internals, OZ Piega Rims, Brembo RCS19 Brake MC, Brembo Radial Clutch MC, Radial Brake Brackets, Brembo Monoblocks, Galfer 330mm SBK Rotors, Brembo Underslung Rear Brake, GPR High Mounts, Woodcraft Rearsets, PC3 USB, Dynojet Quikshifter, RobbyMoto Quick Action Throttle, Hotbodies Undertail, 520 Chain 15/41, Scotts Steering Damper, SS Lines, Pinch Bolt Res Mount, Keyless Gas Cap & Ignition, Flapper Valve & Soft Rev Eliminated, Rizoma Bar End Mirror.