Most definately run the FS. I wouldn't have bought the standard ZX5 in the first place TBH.
Use this setup
http://www.petitrc.com/setup/kyosho/...PR20090621.pdf
as a starting point.
Then do the following changes :
Run lime green springs up front, 1.2mm x 3 holes pistons up front, 1.3mm x 3 holes pistons up rear.
Cut as many rows on the outside and inside of te front tyres as you need to make the car easier to drive.