unless you're specifically aiming for a particular level 4 sorcerer spell, i'd probably go 9 cleric/6 sorc. level 5 cleric spells have some pretty nice options imo. i mean, if dimension door and greater invisibility are things you were really dreaming of, then go right ahead, but i think level 9 cleric is pretty good... it gives you 3 more prepared cleric spells, access to restoration (which basically is the "fix everything that doesn't need wish" spell) and raise dead (if you can't raise someone immediately because you lack spell slots, time, or components, access to this is a pretty significant thing).