This thread inspired me to go with a shorter final drive ratio, which I'm now in the process of acquiring the parts for. Already have my IS300 carrier, just got to source the gears and then it's off to the diff shop.
One thing I've noticed is that people are concerned about running really high rpms on the highway after installing shorter gears. That may be true for the manual, but for those of us with automatics, swapping to a 4.556 final drive has you running right around 2500 rpm at ~70 mph. The reason for this is the AT (which is an Aisin A960E) has a
really tall 6th gear (.582).
I got started researching this because I noticed that on the stock final gear, I run < 2000 rpm at 60 mph, so I realized the gearing between the MT and AT had to be different, if only for 6th gear.
Long story short, I may be looking at going to 4.88. 65 mph at 2500 rpm, I can live with that.
