I had a quaife diff fitted in my old car and it totally transformed it. I can't speak for the mapping, but the diff you will not regret.
It like this; you a buy a massive new hd telly. It's awesome, amazing picture, does all the tricks. You watch films on it and think it's the bees knees. THEN you get a 5.1 surround sound home cinema set up to go with your telly. You realise you were only experiencing half the excitement of your favourite films. That is how the diff is...
