I've done three 4k mile runs on my 2k Savage (MN-FL) and it's not the most comfortable chair on the highway. That being said, it went down the road to Miami in August without a hitch. I have made many changes to my bike however that have made it a much better distance ride.
http://www.bikepics.com/members/jazzcarter/00savage/5 gallon Harley tank up front.
4 gallon aux. tank on the back
V-Star saddle seat
Cheap Harley 2nd party floorboards
The largest NationalCyle fairing style windshield
Saddle shaped gel pad that is a marginal improvement
Check your cam chain adjuster. Make sure it's not about to fall out and let your chain fly.
Make sure your battery connections stay tight. I sat for quite a while by the side of the road one day wondering why it would run and quit, run and quit.
Get off the bike every couple hours for a couple of minutes to stretch out the legs. It helps on some of those 600-700 mile days should you decide to try for them.
Drink lots of liquids. You dry out really fast. Gatorade is a life saver.
Run synthetic oil. A cooler engine is a happier engine.
Ride the back roads and take a camera.
There, I've said my piece. Just get out there and do it.
Jack