Can anyone who's driven both comment on the difference in gearing -- ET's 0-60, 1/4, responsiveness, driveability, top speed, etc.?

I was surprised to see in a different thread that the 5 MT is offered outside the US.

 

The 5MT is only offered with the low-power engine, so there is no direct comparison on performance. You should check on the Miata forums at www.miata.net, since the Miata is offered with a 5 spd or 6 spd behind the same engine!

Regards,
Gordon

 

6mt is better than 5mt in terms of performance driving. 6mt offer superior control over your powerband. However 6mt is inferior to 5mt in terms of 0-60 and 1/4 mile, because you have to shift 1 more time than 5mt, loosing tenths of seconds. Explains why Evo(5mt) and Sti(6mt) has around the same 0-60 and 1/4 times despite a 29hp difference! and similar curb weight.
On a real track, 6mt shines over 5mt. I believe s2k, 350z and rx8 would all be a tad faster in a straighline if they are 5mt. I dont think it affects top speed, which has more to do with factors such as areodynamics, stableness of chasis, displacement and how high the engine revs. In terms of everyday drivability... they both suck :p i.e. getting stuck in a stop and go traffic jam can get really annoying fast.

 

Nope - what's the speed at redline in 2nd gear of the 6MT car? 65 mph at 9000 rpm. 0-60 is achieved in 2nd gear whether the RX-8 is a high-power 6 speed or low-power 5 speed. No extra shift for 0-60 in the 6MT.

(Reference - Road & Track Road Test Data Panel, Speeds in Gears )

Regards,
Gordon