Allegedly Kevin McBride is 6'6 with an 80" reach. That's according to BoxRec. His reach is pretty short for a guy that tall though. Normally guys that tall have at least 82 or 83 inches of reach. Fury, who is realistically about 6'7, has an 85" reach. Manny Steward said that it's actually longer than that which I wouldn't doubt. He would know.
I agree with Holmes. Fighting rangy opponents that are significantly taller does tend to be more challenging. Even an untrained beanpole can make a much shorter man's punch miss his head simply by leaning back as it comes in. Boxers would be well-advised not to do this, instead they should use a proper layback, but many did this and still do to this day. Muay Thai fighters often utilize it to dodge kicks and other incoming strikes. It can be really effective even if it can be dangerous.
Yeah, giving up several inches in height is more difficult but it becomes especially difficult when that person also has a long reach to go with it. You'll have to constantly punch upward as the much shorter guy and will have to work harder just to get into range. Boxers are taught to try and bring the taller man's head down by going to the body but that's not easy to do consistently. When attacking their head you'll have to punch up whether you like it or not if there's a significant height difference.