.. the car is a brute! i guess if you're very serious in modding ur car and all, a Rex STI would be ideal. gonna be very costly, but if you've got the money..the sky's the limit. and it's probably easier to find parts too since it's more common. oh yeah, since it's a 4 door..not so cramp lar (instead of RX8's suicide doors which does look cool tho)
but you're into more stylish (curvy) kind of car.. then i think the RX8's for you. it might not be super fast (even if you mod up) as compared to the Rex, but it's still sweet. i've seen quite a few RX8's been done up very nicely. then again, some ppl might call it a chic's car. but heck, i love the 'sports' look
So, IMHO..If you like to distinguish yourself from the rest, the RX8 is good as it isn't as common. but if you love the grunt from a boxer engine and show off your muscles, the Rex is for you. I would still go for the Rex as I'm a speed head. :)