The route you found is the base of what can be extended into a longer route with more climbing. I have rode in this area for 20 years and the bike shoulders, especially when you cross the county line on Spring Lake Highway are a blessing compared to the old days. FLvector is right that some people think they own the roads but for the most part, especially on Sunday mornings, not that much traffic.
You can extend this to 53 miles with 2500 feet of climbing with the following 3 adjustments:
1) pass Church going straight on Spring Lake----make a right on Hickory Hill---go until it turns to gravels and turn around---nasty climb both directions, then when come out, make right again on spring Lake
2) After a steep downhill on Spring Lake make a left off of Spring Lake onto Olympia (unmarked here but it is between Powell and Rt 98. then a left on Neff Lake which takes you back to Powell road. Left on Powell back to Spring Lake--make a right here---retrace to Church and make a left---back on your original route---this gets you two steep hills on Neff Lake road
3) at #15---the little gas station---, make a left to head out to Trilby---several good hills here---this is an out and back---instead of going all the way to Trilby though after about 4 miles when heading straight east you will see an entrance to a subdivision---take that left and shortly you will face another steep climb---at the top turn around and re-trace back to your original route.
These extras hills enable the ride to quickly accumulate the extra climbing of this route. If extended further can be useful when training for longer races or centuries in the mountains in places such as NC and CO.
Enjoy the area!!