If you really like a US V8 by all means get one of those instead, since you might risk regretting your decision and ultimately it's up to what you like best.
Being no fan of Wankels, I'd look elsewhere than the Mazda but that's me. The RX8 can feel more nimble and tends to rotate easier than the WRX, but IMO you can get on the throttle sooner in the WRX. I don't know how to drive an RX8 quickly but people certainly do. In both you have to keep the revs up and the WRX has a 2nd that's too long and too short at the same time, and it can leave you hanging depending on what your entry speed was. It tends to understeer worst at the exit, but I prefer understeer.
Oh, about the Fords -- but everything needs a grain of salt and they're caught up in straight lines there:
My stock WRX vs. newer(yr?) Mustang COBRA SVT