Dual brushless and a spool.

[Serum]

If a spool makes the backside unstable in full power load, a diff would even make it more unstable.

I used 10K silicone in the rear diff of my savage, the problem was, it would takes a lot of pressure from the fronttires, so these can't steer the car anymore. (it just starts living its own life..) now i have got 300K silicone (peanutbutter thickness..) and the truck goes straight. What you can do;

Give the rear a little toe in (3 degrees or so), and a 0 degree chamber (or if you have that, give it a few degrees chamber)

And no, RD logics are just too short for the 1/8th diffs.

It takes UE's or MIPS (Mike has got those MIPs and i heard/read more better stories on the mips than on the ue's..)