6" and bigger is a fabulous start no matter which way you fall.
the bigger the telescope the brighter things appear. allowing you to see fainter objects.! easyest way is to look at how much you want to spend, and hit that range.
10" will be too expensive unless your 100% sure thats what he wants. a 8" isn't bad and like you said can be had for 440. (good price) and the 6"'s for between 300-400 generally! we could go into all the specifics but like you said analysis paralysis!