What would be an ideal gear ratio setup for an RB25DET engine for a quick acceleration, pretty good midrange, and alright top end? (I'm mostly going for the acceleration part as I'm looking to set it up for 1/4 mile.)

The only aftermarket gearing for the Skyline that i know of is OS Giken. You can buy Cusco diffs but not sure on the available ratios though.

The OS Giken gear sets come with three options. A, B, C. A would be closest to factory rations while B would have a much longer 1st gear nearly 100kph then closer 2-5th gears. Not sure on C but from what I've heard it is more a circut ratio not a drag ratio.