RX7 brake adaptor brackets -

[Ozone]

Why is it bad that the piston area is the same as the original caliper?
You have to balance changing of piston area with disc size to get the brake balance you want (ignoring bias adjustment via balance bar or pressure regulator).
If you want to keep the same rear brakes and fit larger front discs then you should reduce the front piston area.
If you want to increase the front and rear disc sizes you might want to keep the piston area of the front caliper the same.
The RX7 4 pots are alloy so are lighter and also you should get better brake feel (they should be stiffer but don't assume an alloy 4 ot is automatically stiffer as aluminium is not as stiff are steel) and pad wear will be more even/reduced.