Here's pretty good evidence that it won't.
http://www.rcuniverse.com/forum/m_27...tm.htm#2721707

Your %age calcs are correct, you can expect 13% more speed with the new clutch bell. Your starting point of 38mph is wrong. A stock geared evader, in perfect tune, on a perfect day, on a perfect surface, will only reach 34mph. On a good day you're likely to see 30. Which means your new bell will give you 38.5 on a perfect day, and 34-35 on a good day. If you get the bx 56 tooth spur, you can expect 37mph on a good day, and 41 on a perfect one.

You can download [link=http://www.rctek.com/pdf/rcgears111.zip]rcgears[/link] and do the calcs for yourself. The evaders transmission ratio is 2.89 and it's engine will rev at 30k (estimated) on a good day, and 33k on a perfect day, perfectly tuned. The stock tires are 4 inch diameter i believe.