I am very disappointed in the initial take off of the CRD, especially when towing and in heavy conditions so was looking at using the 4.6s to gear down for this. Currently I am running 4.1s and 33's so I am not helping myself much

The approx 10% reduction in gearing with the 4.6's would be offset in 5th by the 10% increase with the Marks overdrive.
As I see it I would achieve lower gearing for take off and going through the box but would get back to approx factory setting once in 5th.
I could of course run 35" tyres but that would not help with the initial take off.