I had a RX8 for 4 years, pleasantly modded and owned from new. The RX8 is bags of fun, very nimble and very, very chuckable around the twisties. The TG track times are very similar, which can either mean something or nothing, I like to think that it represents the real world, bends and stuff. The 350 and the RX8 posted the same times, so they are similarly matched on a typical road.
Put some talent behind the wheel of an RX8 and a driver such as one with my ability in a 350 and there will only be one winner, not me!!
That said, the biggest reason, apart from a lack of updates and facelifts etc that convinced me to sell up was that the RX8 lacked one overwhelming factor, that was torque, but then again the wankle needs to be revved. For me the lack of torque was most evident on two occasions, going up Stelvio was one, another was when a 350 left me for dead, going backwards, felt like I was in a peddle car, on the straight.
The RX8, even the R3, has had it's day, well past it actually, the fuel consumption, depreciation, flooding etc.., and the lack of Mazda support together with pitching the car at blue collar levels meant that it was never going to be a classic.
I had tremendous fun and many happy memories in my RX8, but there are better cars out there and if you're not fussed by a two door, two seater, the 350 is a great car, bit dated now IMHO, but with a few tasteful mods, can be made to look very up to date.
Sadly, your RX8 is worth F all, so anytime is a good time to get rid.
Oh BTW, this club, as you've noticed, is free to all, unlike the RX OC and I don't have a 350, but a 370, an altogether different fish