I have a f-250 6.7L. Engine noise is the same as gas, and I have put 40k hard miles on it. No problems thus far.
Stay away from the early 6.0's and 6.4's. The late 6.0's were good, we have one f-450 6.0 and it has been good to us.
You can also plug in a 6.7 in the winter time to keep it warm when it is not running.