Yes, it is - one reason why I have the 3.9 is that I have a sequential gearbox with 1:1 6th gear and using a 1:1 6th gear with 4.08:1 FD ratio is too low (Vmax @ 8000rpm with 285/655 slicks, 1:1 6th and 4.08 FD is only 245kph whereas with 3.9 FD it is 256kph).

With the OD Nissan MT6 box, I use 4.08:1 .. when the sequential goes in (it is in my historic race car at present), I need a slightly taller FD ratio.

Everything is a trade-off