XRAY - Model racing cars

Dear Guys,

I just bought my own XT8 '09 specs. I immediately converted it to Brushless with A MMM2200KV set, a RC-monster motor mount, Vorza battery tray, Vorza ESC mount, and a 13T pinion for running 4S. I run the diffs 10K front, 15K center, 7K rear from past experience.
(pictures will follow)

At setting up the car I noticed a rather low ride ride height with the standard springs and pre-load. After weighing the car I found out it weighs 4350grams. That is almost 400grams or 10 percent more than the nitro setup.

Question is: should I adjust ride height by preload or should i buy harder springs (higher spring rate) and should that than be the violet or the purple ones??

FIRST TEST RUN: 13 pinion is rather small, everything stays relatively cool, top speed (with proline badlands) is 40 Mph, center diff gets really hot from 10 min test run (with quite a lot of fast acceleration)
so the changes will be (probably apart form the springs, that question remains; did not do any jumping):
14 pinion
20k center diff oil

thanx for the help!