It really depends on what sort of driving you will be doing. As far as I am aware the s80 (from the earlier tegs)/s4c gearbox have the same final drive, so I don't think you will gain anything from swapping.
If you go for the later s80 teg box, then it will have the 4.7 final drive. Gives you a bit more acceleration and slightly lower top speed. My personal preference (I think I've got a 4.7fd at the mo), I'm putting the 4.4 fd back in. I do a few motorway/A road miles and the car is revving pretty high. At 80 it's already past 5k rpm. Probably doesn't help with the exhaust I have on at the mo which is pretty loud. Also, mpg will be higher. Again, if you have an exhaust which isn't too loud I'm sure it will be fine. If you do a lot of track days or just town driving I'm sure the 4.7 will serve you well.