Synthetic also provides better protection at high RPMs which our cars see often (At least mine does). I woudl recommend staying away from Mobil1 as it seems to be thinner than most oils and several people have burning problems. I woudl look into Amsoil, Redline or Royal Purple.
BBQd00d makes a good point too that use the best you can and change it often. Consider what you put your car through when judging your change intervals.
Trey