You'd still need a spacer or coilovers, even on the NB right?

Don't believe so, but i'd recommend you contact Emilio.

225/45-15 tires on 15x8 or 15x9 rims "might" need 5mm to 1/4" spacers if you run excessive camber up front and/or have shock springs in excess of 70mm or so. Without spacers I rub the Tein Flex springs on my NB with -3.0 degrees of camber at full lock with either 15x8 or 15x9 rims and 225/45-15 tires.

https://www.miataturbo.net/showthrea...t=45083&page=2

tilt at one point had a pic of the RE11 in 205 compared to rt615 in 205 and they looked a decent amount wider.

Gay. I used to love the RT-615's until my 7th or 8th set. They hate heat cycles and they turn into rocks about the third one in. I switched to the NT-01's in 225/45ZR15 (with 10 mil spacers). I can run good camber all around, they heat up fast, withstand multiple heat cycles and they're still in the same class as the RT-615's (up here for local SCCA). They may not last as long as the RT-615's, but taking into account the lack of heat cycle resistance the Falken's have, the NT-01's last longer and are way stickier. Plus you can shave them OTB if you want.