Mmm...ok...interesting then!
Well the extra weight I put in was because at Caldicot indoor...running on medium/high grip carpet and a fair bit of polished floor the car lacked grip all round on the slippy bits without it. The extra weight all round helped a lot with that, although I have changed the damping dramatically since then, so may try a lighter car and see what it does now.
The other factor that was based on was both the other mid motor cars I've ever owned (X6 & Centro) have both needed to get up to the 1600-1700g weight mark to get balanced handling, and I've heard the Durango is that kind of weight without adding any extra weight, so figured it was a fair shout that this car could also benefit from it.
So far it has...but more testing as I/we develop the setup will prove or disprove that for sure!