RX-8 is quicker IF it has a manual transmission. If automatic, the Maxima is quicker.
They both reach 155mph.
The Mazda handes much better, but cannot be driven in snow and is slippery in rain, while the FWD Maxima does not have problems with that.
The Maxima is more practical, more reliable, cheaper to fix or maintain, more luxurious, more comfortable.
So overall, the Maxima is better.
But for the race track, the Mazda is better.