Making short rides to your job or local supermarket and riding several hours long are totally different things. When the final point is not far from the starting one, all you need is general comfort, but in long hours “iron butt” rides many small things you may have not mentioned previously become particularly important.
If you plan to ride for 20 or 30 hours, there is a series of questions you may ask yourself. First, is your bike good for that? If you are not feather-light, you know how inconvenient smaller sport bikes are. You simply won't get rid of the feeling you’re too big for this bike. On the other hand, too big and heavy bikes are not a great decision either. I saw many riders larger and heavier than me, who stopped their heavy bikes at parking lots and dropped them due to exhaustion. Determining “your” bike is not that difficult – just visit any big retailer or motorcycle exhibition, sit on each bike and imagine you will remain in this position for many hours. Will it be a convenient ride?