Consider searching for a thread I started awhile back for on the same topic. It is always a hard decision if you're looking to travel a distance of 5-9 hours, IMHO.

In your case, since you have to rent a car, it is probably cheaper just to fly (unless you want to have a car anyway at your destination).

No one here can tell you what to do. You'll just have to figure out how you value your time and money.