Doh... forgot about circuit racing...the way you asked the question was really vague, circuit is similar to time attack.... so you are using a stock SE-R SR20DE trans from a B14 chassis and need shorter 3rd and 4th gears for the track. What is the highest RPM you get to in 4th though on the circuit?
http://www.sr20-forum.com/340487-post1.html
Here is a link to a PDF that contains all the info you need for your gear selections etc. If you need quicker acceleration, consider running a smaller tire size, otherwise the next fastest gear set would be a trans from an SR16VE, or convert to 6 spd and get really nice acceleration due to the shorter gear ratios.