I didn't think I'd get you to bite on the single lane gravel. The tar that goes though that state forest is the best section of road I've found on the east side of Iowa though, it is one of their byways. I put a suggested route from Gays Mills to Dubuque using mainly Iowa roads as the only road I know from there to Dubuque well is WI-35 and it is BORING along that stretch. The stretch from Guttenburg until you get on 52 to head into Dubuque is my 2nd favorite stretch on this side of IA. The view from Balltown is incredible considering it is IA, there is an overlook that is something like 500 feet above the mean river level or something. The overlook itself is not that great, it just looks down at some farms between the town and the river about a mile from town but the constant views along the road are great.
I'll vouch for Canada Ridge Road that Aasland mentioned below, just don't do what I did and take a right on Waumandee Glencoe Rd, it turns into Schaffner Valley Rd which has one of those nasty "Pavement Ends" Signs on it 3/4 of the way back to county G.
Something kinda fun if you head south from Gays Mills would be to hit up cassville and ride the ferry
(Click Here) across the river to iowa, that puts you on Great River Road Iowa just south of where it gets real fun heading towards Balltown.
Route
If anyone has some routes from Gay's Mills or Richland Center to Dubuque I'd like to see them too. My scouting trip for that section this spring got cut short when I broke my GPS cradle trying to fix my XM that had cut out and got a flat tire a half hour later. I was heading to Dyersville to snap a photo by the town sign for a grand tour I'm doing before I headed into WI to check that area out. The flat tire was the last straw on that trip, I wasn't enjoying myself so I fixed the tire and grabed some boaring strait roads and booked it home. That was my last scouting trip this spring for that rally and we had a little hole in the bonus locations.