Spool = better traction
Spool = more broken drivetrain parts
Spool = crappy steering

Open Diff= better steering
Open Diff= less stress on drivetrain
Open Diff= ok traction

Open diff with thick diff fluid= great traction
Open diff with thick diff fluid= good steering
Open diff with thick diff fluid= less stress on drivetrain

So which would you choose? I would say open diff with thick diff fluid to get the best of both worlds. Why make trouble for yourself and lock the diff. Locked diff is great for traction in straight line. Not for bashing or racing.