With Time Comes Opportunity
You could make the drive from Cumberland to Lincoln in as little as two days if you stuck to the Interstates or even (shudder) the Turnpikes. But with four or five days you have a real chance to get off those very well beaten paths and experience a good bit more of slower paced travel, including finding the random honkey-tonk on the way. I'm going to suggest that you start on the old National Road (US-40) right in Cumberland and basically follow that all the way to Indianapolis (using beltways around cities like Columbus, Dayton and Indianapolis of course) and then switch over to US-36 through the rest of Indiana as well as Illinois and Missouri. At Fairview KS turn north on US-75 to NE-2 for the final bit into Lincoln. Taking such a route will go a long way towards putting you in touch with both the outdoors and local watering holes, certainly more so than sticking to the superslabs.
AZBuck