We use the Stock Throttlebody On the RB25 Powered 180SX Sportsedan I work on and never had trouble making 600+rwhp.
All you get from a large throttlebody is poor throttle control, I did a Power run on another Skyline Racecar with 90mm Throttlebody, at 20% throttle
the car made 440rwhp, This car was very hard to drive on the track so we went back to Stock 25 Throttlebody, No powerloss at all but Lap times were faster and more consistent.