I've owned MANY Miatas and MANY Jackson Racing (Sebring, Downing) Superchargers. I've ran them @ 6PSI, 8 PSI, 10 PSI, and 12 PSI. I've ran different size nose pulleys, crank pulleys, water injection, intercoolers, and all sorts of intakes and cross over tubes. I've purchased them used as well as already installed on cars that I have purchased. I've destroyed quite a few and sold quite a few.
Most of the information contained on the SuperCharger pages is from around 2002 - mid 2005 when I switched from a Supercharger to a Turbo on Red Beast. The Supercharger that was installed on Beast @ 12 PSI was pulled and installed on what was then my wife's Smurf Blue Miata @ 6 PSI. We later upgraded the car to a Link ECU and upgraded to 9 PSI. For some reason, an M1 Miata with a JRSC @ 9 PSI feels much better to me than an M1 with a 15 PSI Turbo. I really regret pulling the JRSC off the blue car and will probably purchase another SC'd Miata in the future.
There is quite a bit of work to do to the JRSC pages here so it may take me a while to get them all sorted out. If you have a JRSC I highly recommend taking a look through the www.sebringmiata.com mirror I have. Luckily I snagged an almost complete copy of that website before it was taken down. I never have been able to get a complete copy but I believe what I have here is about the best copy that currently exists. Enjoy!