I tested both of them the same day. I tried an autostick crossifre and did NOT want the car at all. Then I tried the RX-8 manual with every option (grand touring). As soon as the test drive was over I inquired about aftermarket leather to replace the horrid interoir ($1200) and looked into a aftermarket front end ($1000 plus mounting and painting) because is looks really, really bad. Those two parts of the car where awful but could be replaced.
The mechincal issues I had with the RX-8 (note I am a former RX7 owner) was that there is no touque and the car drove like a granny mobile unless you where above 4000 RPM's. Then there is the part where you must make sure the car is fully warmed up before you take off so that the engine does not flood (a $100 mistake) and that you have to constantly check the oil level. Mine use to burn 1/10 of a quart every 3,000 miles and they told me it was more like 1/4 of a quart now. On top of that the oil pressure gauge is useless and told you nothing. The car really needs help in the low rpm range and the previous RX7 had a twin turbo where one helped in the low RPM's to help deal with this.
All in all the car is a pain to maintain and smells of oil bad after you have been pushing it. They did not even put in a limiter or beep at you at redline like they did in the past (yeah it is not a conventional engine and it is hard to tell how close to redline the gerbal wheel is getting). Hope you never get a coolent leak either, so check the hoses all the time or it may cost you a new rotary engine.
My RX-8 overall review summary:
The RX-8 looks like a frog, looks too long, need that horrible nose replace that make it look like a bucked tooth rabit when a licence plate is on it, has a horrible leather trimed interior (the rest of it is not much better), has nearly unsusalbe rear seats (you have to lock your feet under the front seats), runs like crap at low rpms, has no trouque, has to really warmed up before driving it or you will have to replace the spark plugs, constantly needs oil, smells of burned oil after driving the heck out of it, the options for the car are way too much money, gets horrible gas mileage and the exhaust sounds like a weedeater when you drive behind one.
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When it was said and done and the RX-8 with the aftermarket parts would be more than the crossfire or the 350z i decided to go back and try a manual crossfire in hopes that it would be different. The difference between the autostick crossfire and the manual version was like night and day for me. The rear end of the manual version is all over the road, I could not get the autostick to do this.
I picked my crossfire over the 350z and the RX-8. If I needed a sedan I would have picked the RX-8 over something like a Nissan Maxima and just modified it.
-marc