i believe that the ct4s comes with these ratios as standard: Spurs 42/38 teeth, Pinions 15/20 teeth - 1st gear/2nd gear respectively. Second gear is the tallest (highest speed) ratio there is for the cen.
There are quite a few combinations that u could use tho. have a search on the net for the ratios available, just remember to be sure they will mesh ok. if u have a diffence of 4 teeth between the spurs, u will need a diff of 4 teeth between the pinions if u see what i mean. (usually - as u can see by the standard ratios is a little u can get away with - 20t - 15t = 5t diff, make sure u are spot on with this or at least very close indeed, and u should be ok)

smaller pinion and/or larger spur = shorter gears
larger pinion and/or smaller spur = longer gears

so ur only options are to go with shorter ratios (better acceleration) or to make the gearing of 1st gear closer to 2nd. I found that 14/18t pinions on 42/38t spurs was a good compromise between speed and acceleration on my rally, although i have now fitted 16t/20t with the same spurs, cos my .18 is still spinnin the wheels too much!!

www.cenracing.com has most ratios available, get the part numbers and run a search on those.

just a small point - when setting your gear mesh, check it at 90, 180, 270 and 360 degrees on the gears as they are not always perfectly circular im afraid.