Refurb rims, add spacers and new tyres...opinions

DeanoL

Hey everyone, looking for some input and opinions on setting up the wheels on our 2012 370Z Coupe.
Before we start, I have thoroughly read the wheel fitment thread and the "will it fit" thread along with a number of others, so I am not blindly asking lazy questions. Using all of those threads I have put together what I believe are the best options, but I would still appreciate some opinions of others who know a LOT more than I, just so I am 100% comfr4otbale with my choice in the end.
So as far as the car itself, it is stock height, nothing at all done to the suspension and nothing will be done, its not worth lowering here in my local area in Australia, the potholes our council consider acceptable are about the same depth as a swimming pool. So.....the height shall remain as is.
As far as spacers, after much back and forth, I have settled on Eibach 10mm front and 15mm rear, BOTH are the stud replacement type ( I want to use the best options). I selected them because I dont want ANY tyre hanging outside the guards, I do like the flush look, but I like a meatier tyre look too and I want the sidewall to be flush with the guard, not the tread. There is a blue Z on here with the same setup and it looks good to me. So I have settled on that.
As far as tyres are concerned here is where I am looking for a little guidance or opinion. Due to me preferring the meatier or more square look tyre fit ( I absolutely HATE that stretched tyre look), I figure along with the above spacers, if I go up a size on my tyre it may also fill out a little bit more of the guard in both width and height.
The rims are the sports rims (Rays??) which are 19 x 9 front and 19 x 10 rear, with 245/19/40 and 275/19/35 tyres fitted respectively.
We like the rims so we are going to take them off, have them stripped and powder coated bronze chrome. The car is red and whilst the wheels are being done I will do the brake rotors and door handles in paint matched red. In my mind it should all look great when its done fingers crossed.
So using the tyre fitment calculator you all use, I have come up with the following and its the rear tyre I am not sure about in terms of which is more ideal. I have learned its mostly about diameter matching, so I input the very base model wheels (the 18inchers), then my current sports rims and then the new slightly meatier options and the measurements are as follows. What do you thin the best rear tyre selection would be in order to have matching diameters front and back or to stay as close to original diameter as possible. Going back and forth between the base/current and the new slightly wider options has me unsure which would be best. Any and all input from you guys greatly appreciated and thanks. ITs a great website with some extremely valuable info and people. Please see the attached specs so you can see what I am banging on about.
My main question is....am I better trying to get the new tyres to be a closer match to the base models diameter or trying to get closer to the current sports wheels diameter?? My line of thinking is the base specs are the base sepcs so they are what we shoudl aim for, as the sports rims are already different specs diameter wise.

Attached Images

Tyre options and info.png (60.1 KB, 9 views)