I know this is regarding road biking and not MTB, but thought I would share.
I found a way to link the Greenway, Palmetto Parkway Path, and the Walnut Grove Greenway into one loop around North Augusta. Its roughly 20 miles but you could extend it. I cut the Greenway a hair short because I had to get to work. But this is a great early morning ride and the vast majority of it is on bike paths and not busy roads, which I like.
There are some nice hills going up the Palmetto Pwkway. This loop starts and ends at my house, so please do not start there unless you would like to pay a $15 parking fee ;D
Mainly just 5 notch for a mile or so... But that section is down hill if you go CCW... and I'm cruising at 30+mph and traffic wasn't much of an issue. The road is fairly wide through there as well and people could pass me without any issue.
Hwy 25 at exit 5 has a nice wide side walk, so no traffic issues there..... You do cut down Beauna Vista (sp?) by the old police station to get to the palmetto pwk, but that is 30MPH with very little traffic. ( this section looks strange on google maps images because they are out of date in the photos, there is a new road )
Other than that... its all bike path. The Palmetto Pky is all bike path, with nice hills.
I'm willing to show anyone in person if they would like to do the loop...
Now that the Greenway has been extended all the way to Bergen Road (frontage to I-20) it is even easier. You can cut down Austin Graybill Road and shorten the route. Or cut through Bergen place neighborhood and get to Gregory's Lake Rd and go down Walnut Lane.
You can make this anywhere from a 16 - 24 mile loop around North Augusta.
This is the loop I used to train for the Augusta Ironman