gearhead_318

iTrader: (1)

But since a Miata weighs less the a mustang, the T5 should but up with a lot more power, right?

Full_Tilt_Boogie

iTrader: (1)

Yes.
The domestic worlds views on transmission strength is very, very different than ours.
They're breaking T5s with 3000+ lb cars usually running on massive sticky tires and being as mean as possible to them.

Wildanimal

iTrader: (2)

Back in my mustang and Camaro days, t5's were a frequent fail part but so was a 700R4 auto. V8 torque and the weight of the car have to play a significant factor in durability.

The T5 should stand up much better considering the weight of a miata and the lower low end torque numbers of the turbo cars.

NiklasFalk

iTrader: (1)

The "wide range" Quaife (QKE3K, 2.564 1st and 0.794 5th) is still available and will be available for at least a couple of more years (according to the Quaife rep I talked to at Autosport last weekend). £1476.00 plus VAT isn't dirt cheap though.
With the Quaife and a 3.6 you get 1st identical to a 6speed 2nd with 4.1.

With my 4.875 I would with a Quaife set get a 1st that's taller then the 6sp with 3.6 (which I know is on the short side even with stock power from the 03 I had to 8 years). But I'm far from the torque range to have issues.

A 1st of 2.2-2.6 seems to be what's wanted.

Edit: What about this wide gear set for the T5?
http://www.gearboxman.co.uk/infot5.html

Ok, getting a new box and then start to modify it adds up. I'ts easier to convert a 6sp to a 5sp with a dogleg "1st"