Really? Another Miata thread....

[Jake]

I'd build the car for ST5 and see how it goes with local competitors. Nationals is a fun idea, but it's expensive and can be very far away depending on the year. Focus on where you spend most of your time (regional level) and how much fun/competition you can have there. Ideally that would translate to the national level. As you say, you can always protest with data if the first year doesn't go so well. But in the meantime, 5 is really your best option if you want to keep the car.