Wheel sizing/offset discussion (not flush/fitment)

[Giannino]

When I first got my hachi, I had aboslutely no idea what kind of new rims I'd need. Asked a guy at a local tyrepower and his wheel sizing chart and it turned up (from him) to be my nice 15 inch rim X 6.5 +40. Now +40 you must be thinking im smoking something to put +40's on a hachi, but honestly at the time, going off his book and him inspecting my car and its current rims I had no reason to doubt.

Now my new 550 dollar a rim set of 5 watanabes (yes I got the spare too...) arrived and BAM instant problem. Already needed a spacer for the rears to fit but even after removing the front stock suspension and putting vastly more space efficient D2 coils on it, front have zero chance of fitting. Ive seen the wheels thread and its basically full of fitment and negative offset stuff. No help there from what I saw.

So does anyone have good sizing estimates for a 15x7 rim WITHOUT ROLLING THE GUARDS OUT OR SCRUBBING. Ive been looking really hard and I've found so far people suggest 15x7+20 offset for good inner clearance of the suspension and ample enough clearance to the guard without scrubbing in turns. Good Idea?

Also I guess looking to sell a set of Brand Freaking Spanking new Watanabe 15x6.5+40 Rims lol... So if anyone happens to have a Miata, or some FWD car that could use a set of new watanabes here I'm ur man XD

Edit: Though people telling me also that just 15x7 zero offset will still be inside the stock fenders with a reasonable degree. I thinking +10 maybe for practicality's sake and give some much needed high speed pothole suspension travel (roads here a shithouse).