On my 'home brew' mid motor B4 thingy I tried 3 gear (without having to reverse motor direction) and 4 gear. Of the two I prefered the 3 gear for the reasons Rich has stated, and we have chatted about it in the past.
The last time I drove an X-6 it was a 3 gear, now I have returned I am driving a 4 gear. I have to say it feels very much as I remember, I'm not sure why the X-6 is less affected by the change (well I have a few ideas), but if I'm honest I don't care. The car is good and I'm just going to get on with driving it now........
........ or trying to fit a 5 link rear end!
G