I'd asked this question a bit back. Well, I was in the process of ordering my chip today and Steve answered the question.

> On the 3.2 Carrera, the difference in output between 91 vs 93 programming
> is
> about 3-4 hp from 4500 rpm up, because the 93 programming allow about 2
> degrees more ignition timing advance. The low and mid rpm torque and
> throttle response gains between the two chips below this rpm are virtually
> the same.
>
> With chipping, you can always run fuel equal or greater octane than a chip
> is rated for. In other words running 93 with a 91 chip is absolutely
> fine.
> But with the 93 chip, you should always be using 93 or greater octane, not
> 91.
>
> Under your circumstances, with 93/94 available everywhere, going with a 93
> programming is a good option. The problem is 2/3rds of the USA only gets
> 91oct at best. Let me know if you have any other questions.
>
> Regards,
> Steve Wong