I Re-Geared my Cayenne from 3.55's to 4.56's. This change is a 29% difference in gearing, while 35" tires are a 20% change from factory. The over correction in gearing actually resulted in a loud drone when driving on the highway at 70+mph due to the increased revs. I actually removed the diffs and swapped in the old ones shortly after when the new front diff started whining and did not put the old ones back in.

For anyone else contemplating this, I recommend keeping stock gears, or going to a 4.10 diff set from ma GTS or a Titanium package 955.