Ah the ultimate quest!
Studs are 4 x 100 (PCD)
Standard wheels are 6J (width at rim) with an offset of 43 (et)
Chris's red demo car has
front 7.5j 20et
rear 9j 15et with a 25mm spacer.
I think 17" rims are a bit tight, but if you have real low profiles, like rubber bands, you may do it.
Loads of stuff on the Mazda forums like MXnuts etc
On the rear from the Mazda hub to a plumb line to the wing edge is six inches. Deduct one inch for the wheel arch lip and you need to make 5" (127mm), which I suppose is on a 9j (228mm).... 228 divided by two is 114, less 127 is -13mm offset or ....well now I have confused my self, but zero et on the rears would do it.
This site is useful...
http://www.willtheyfit.com/
Also, if your thinking of going bigger in the tyre department......
http://ejelta.com/tiresize/index.html
Most of the Ebay alloy wheel suppliers cant do a 9j in a 15" so you will have to go up to 16" rims, then you can get almost what you want, and more tyres are available.
You never know what is coming up on Ebay, pistonheads etc.....but I think I am going to get banded steels made so they are justb right with maximum dish.
www.wide-wheels.co.uk
http://www.alonzecustom.co.uk/
cheers,
Nick