Well kudos for not calling us all ********, we probably deserved it. Do a lot
of searching, staggered setups are a no-no for Miatas. They're a very balanced car, and benefit most from a balanced (aka equal) tire size. For an NA, you start running into some fitment issues at around a 225-235 width in the front, and I think
235-255 for an NB, again on the front. You can put wider wheels on the rear since you don't have to deal with them turning, but then you'll just be adding understeer issues since you're now under-tired in the front.
At the 225+ width sizes, you're hopefully putting some very sticky rubber on the wheels, as I don't believe it to be very necessary on the street (unless you're driving very dangerously, or have obscene amounts of power). If you are running track tires at 225+ widths, you'll notice a little of the "throwability" of the Miata start to disappear, and you'll be wrestling with it more around corners.
This is all incredibly opinionated, and I'm sure others will chime in disagreeing and putting in their own ideas about wide tires and staggered setups, but that's my