There are a lot of people who don't fully understand the differences between ecu's, but are more than willing to say that the A9L is the only one that should ever be used.
Was the SCT chip created for your current combo?
What ecu are you currently using?
What are the future goals, and what is your current setup?
There are some minor timing differences between the A9L and A9P, as well as fuel differences.
None of the differences, that I have found, will provide a performance advantage in either computer.
1990 GT - something 351w based... some day