Maybe the best of both worlds would be a conventional 5-speed box in a high torque car and twin-clutch 6-speed with paddles in a low torque car. With one of each in your garage. I got to thinking about this the other day on a fun run in my Mustang. Five gears for the wide torque band are plenty, especially in a modern pony car with an easy clutch and a well-sorted shift linkage. It's fun to use and keeps one's mind and body engaged in the driving.
Driving "a proper 4-speed" (as the Brits would say) was one of the joyous discoveries of my youth. There it was: a ratio right where you needed it, between 2nd and 3rd on an American car's manual box. (The exception was the Volkswagen Beetle--4th on a Beetle was an overdrive ratio of about 0.80:1, useless except for "high speed" cruising on level ground.) A 4-speed was symbolic, too, signifying that its user was interested in high performance driving. (It was around this time that the manual 3-speed was disappearing. Buyers of American cars wanted automatics. Only drag racers were interested in sporty-car 4-speeds.)
When the 5-speed came along, it was icing on the cake: four close ratios and an overdrive 5th for cruising. I used all five speeds in my Mazda RX-7 when I was pushing. Around town, I often skipped from 3rd to 5th.
Now, around town, in my daily-driver Civic Si, six speeds are an embarrassment of riches. I often use 1st-3rd-5th. Or 2nd-4th-6th. The car is happy to start from rest in 2nd on a level or downhill grade. But I have yearned for a floppy paddle 6-speed in the Si when pushing hard on the Dragon.
The Dragon doesn't require much shifting. The Si needs to be in 2nd to pull hard out of a 30-35 m.p.h. bend. But there are short stretches where it's necessary to go up and then down again one or two gears. This is when I'm busy, busy, keeping the car on the cornering line and feeling the grip. Rev-matching heel-and-toe downshifts adds another task my feeble brain can barely handle. It's then that I would love to have a floppy paddle twin-clutch manual that rev-matches downshifts in milliseconds. Click, click: the right gear for the corner, effortlessly selected without the possibility of blowing the shift.
I wonder about the long-term reliability of a twin-clutch manual. There are a lot more moving parts than a conventional box. Would a self-controlled box be kinder to its own innards than a ham-fisted-and-footed human? On the other hand, it would be a relief not to be concerned about an over-stressed throwout bearing or clutch disc wear.
Anyway. I'm perfectly happy--joyous--with the conventional 5-speed box in my Mustang. It's well-suited to the car's character and the kind of performance driving available hereabouts. But if Honda brings back "the real Civic Si," as I'm pleased to call it, I'd sign up for a twin clutch manual with floppy paddles--especially for the Dragon.