The argument of single or double OD for performance is sort of silly. 6th gear is so tall, it's for mileage and cruising, nothing else. If I'm driving my cars in anger, 6th is useless. Both of my cars top end in 5th gear, 6th is just too tall to overcome drag.

With more HP, 6th may become ueseful for sustained speed runs (though even in my 420 RWHP ZR-1 it's not), but then you start to run into the issue of ridiculous driveshaft speeds. If I'm building a car for high MPH, it'll be done with a big HP, a modest OD (not much taller than .75:1), and the correct rear gear to get it done.

Anyone who's ever driven a Viper with their 3.08 gears knows how useless 6th gear is when the car isn't geared for it. Both of my 6 speed cars have 3.42 gears, and even with 400+ HP and relatively light weight, they could use a little more gear.