350-500 miles per day has always worked for me, taking mostly back roads and you can still see things on the way and you don’t feel like you are rushing though. As for road suggestions, I use motorcycleroads.us as a resource for good roads and MS Streets & Trips software for planning the actual route.
This is how I plan a trip:
#1 Figure out how much time you have for the trip
#2 Start mapping out your route until you are satisfied with the result
In Spring probably your best route is through southern US, traveling though CA, AZ, NM, TX, AR, MO, TN, KY, WV, PA
Plenty of good road in those states
