I've got a 4.3 LSD hilux diff behind a reasonably worked CA (330rwhp last time on the dyno).
I'm now moving into circuit racing with a restrictor and will need to go a taller ratio to compensate for the reduced rev range I get.

I use to drag race my coupe in the above mentioned setup and was crossing the line needing to shift into 5th gear just before the 1/4 mile mark at around the 190kph mark. I felt at the time my 60ft time was suffering because of the shorter diff ratio (4.3), whilst great to get a naturally aspirated car off the line, with a turbo setup it didn't really allow the car to build boost quickly enough. It was my feeling that given how light the car was, there was insufficient load put on the engine from a standing start, therefore it actually build boost slower and flow on effect was a slower 60ft time. Not to mention as indicated by others, 4k @100kph gets annoying pretty quickly. I will be rebuilding mine with a 3.5 (or taller if I can find one) but without the restrictor would go for a 3.7-3.9.