I'm 'only' 6 foot with 32" inside leg and always swing my leg over the back. The trick is to have the bike on the sidestand, get your hands on both grips and lean forwards towards them. That will make it much easier to swing you leg up and over the back seat.

I also have my topbox always fitted but have certainly given it and the rear hand grabs a good kicking every now and then.

I'm not quite sure what I'd do if I had a large bag on the bak seat however, probaly mount from the side if I could.