Shafts are the weakest link on an atlas, I change too uprated 21 spline ones on my car.
the 4.6 ratio would be a p100 ratio and quite sought after, I found the 3.75 standard fitment on a mk3 1.6 Capri the best compromise. Still have a top speed of close too 160mph but good acceleration too. My car is 500hp with a standard t5 and 3.75 atlas.