Are you going to the DE event? I plan to run in two classes. I really can't see running the 3-speed in my truck. I already have nearly uncontrollable acceleration (MAJOR wheelies) and super high top speed with my Picco 26 and very tall 18/47 gearing. The motor makes much more power than the S-25. I could probably run 19/47 or 20/47 and still easily wheelie on pavement from a dead stop or a roll. My biggest problem is stopping and turning without flipping over.
On the other hand the 3-speed would probably be beneficial to the S-25. If I were you I would consider a bigger/more aggressive motor before the 3-speed. Your setup will be less complicated and you will have more power on command at all times.
When racing on-road with the Savage (which is rarely) I temporarily lower it by tie strapping the suspension arms to the shock towers.
July 23-24 HPI Challenge in Ohio
August 13-14 HPI Challenge at Blue Diamond Park, Delaware (tentative)*
September 3-4 HPI Challenge at 4 Fun Hobbies, California (tentative)*