Judy,
We ended up changing things around. We lowered the XXL steam oven so that it ended at 42" AFF, allowing us to put a full size drawer below it and started the coffee maker at 42", ending at 60". This allowed us to put a very usable cabinet above the coffee maker with two sliders so that we could reach the back of what would now be a 24" deep cabinet. As with everything it is trade-offs. I think if there were no other considerations at all the ideal height is more or less 42" to 60" and my thought was that bending a bit to use the oven was worth having the coffee maker easily accessible and in optimal location. Having said that, I think ending it at 6' is perfectly fine and if we had gone w/ the regular 18" size oven I am sure we would have done that. Once we went to 24", cabinet wise, it was much easier to either do one full size cabinet below (ending coffee maker at 5') or to keep the oven at counter height and end the coffee maker at 6'-6", which by all accounts was too high. In between was problematic.
Q