OP and I use our cars the same. Not every miata owner that wants boost does 20 to 30 minutes on a track every weekend. I ran 10.5:1 on OEM pistons on the street and drag strip, they worked well. I now have forged 9:1 pistons. But to be honest, if I build another bottom end I'm going to up the compression I think to 11-12:1 range.

JMann, my car is going to be mostly a street car and the odds of it seeing a track outside of an autocross session and maybe a drag session for the lulz are pretty low.

So I guess you're saying it really doesn't matter all that much for that purpose haha. My pistons are probably happy. My line of questioning was more to figure out if you can swap used oem pistons between blocks without having to spend the moolah to have the block machined. It appears that the answer is yes, so I guess I can swap to the 9's if I have the urge to if/when this ever happens. I just thought it would be good to keep the info in this thread together since it's an awesome resource. For someone with an nb2 that wants to run something bigger than a 2560, the info might lead them to swap to oem 9's if they can find them easily.

I think JMan was referring to my comments. The OP is already well underway to his motor build. I was just curious since this thread had great info and I had a few related questions.