I would have to disagree with a few things mentioned here.
I have found that most 6N's I've run are pretty gutless and the 750J's will out-push them easily. There is the odd 6N that pushes good though. Must be chipped differently or something.
Do you like the fast hydraulic speed on the 750J? If you do, then you won't like the slow a** cat hydraulics on the 6N's.
The hydrostatic drive and ability to turn (fast) on a dime is also great on the JD's.
Visibility is good on both of them. JD has better lighting then the cat if you do much work after dark.
I find JD's to be slightly rougher riding than Cat's.
Noise levels in the cab are pretty high on both of them.
6N's are nicer for shoveling tracks with the high drive.
JD's seem to be a bit more 'tinny'. Like rattling doors etc. We've also worn holes through several dozer blade skins on the 750J's working in frost, rocks, etc. Never seen that happen with Cat dozers. Just lots of dents.
It seems that the company I work for has stopped buying JD dozers because the resale value of them is so much less than Cat, although they do have a new 650J on order (requested by an oil company for ice road work).
I usually run a 6T which I like a lot, but if I had to choose between a 750J or a 6N I think I would lean towards the 750J. It's a tough call though.
Good luck
