Final drive ratio conundrum

[DM Clemmensen]

I have a Euro -85 528i

After a long time (2 years) of searching for the right S38B38, the B28 started to show signs of needing a new head gasket, at the least. 
Knowing myself, that would be a complete rebuild with upgraded internals. And throwing cash after that engine would a bit silly, but i can't wait for the S38 either as action needed taking. 
So i bought an M30B35, which I absolutely love btw, and was planning on going full monty on that one. And then indirectly changing my absolute automotive 1st choice (S38) to my 2nd choice, the M30B35+. 
An acceptable life compromise. 

But then, the right engine with the right defects at the right price showed up. Ready for the right nerdy engine builder in Germany to go german on.

So going for the build i have been thinking about since i had my last car of my dreams 17 years ago ( E28 M5) i have almost all details sorted. 
But I can't seem to settle on which final drive to go for. 

Engine is the S38B38
Transmission is the GS6-53BZ which has these gear ratios:

1st

4.35

2nd

2.50

3rd

1.67

4th

1.24

5th

1.00

6th

0.87

Reverse

3.93

As most driving is highway miles at 70-100mph around Northern Europe, lower is better, but then i might as well just drive my E-class diesel. 
So where is the sweet spot for occasional trackdays and daily life?
3.23? 3.46? 3.73?
Appreciate your opinions and reasonings!

[Mike W.]

One would have to drive it to really tell, and even then, different people perceive the right ratio to be any of the 3 that you mentioned. But, stock, it appears the E34 M5 would have had a 3.91 ratio, but nearly 800 pounds heavier than a E28 528i. With the S38 engine etc that might shrink down to only 600 pounds difference, but that's still a bunch. Again, feel is different to different people, but I think I'd go with a 3.46 and maybe even a 3.25. You might even want to do some calculations figuring weight vs gear ratios.

[DM Clemmensen]

Thanks Mike.

The 6-speed E34 M5 had a final drive of 3.23
From which the GS6-53BZ gearbox comes from; The 335i a 3.08 and the 550i with a 2.93 final drive. 

So i will go for a 3.23 final drive, which should give about 2700rpm at 120km/h. 
Should be peppy enough for spirited driving. 

[turbodan]

The first gear ratio in those is quite low. I would go for something relatively tall. A 3.23 would be a reasonable choice. Even a 2.93 would make first gear more usable.