These are all roads I take on a regular basis.
A "quick" loop I do (that I literally got back from 20 minutes ago) is from Katy down I-10 to Brookshire, South on 1489 to Simonton, west on 1093 to FM1458, then north on 1458 through Frydek, back across I-10 to the north side of 1458 from San Felipe to Pattison (and I take a little detour loop on 3318 just after the Brazos River bridge around to Robichaux road back to 1458), then north on FM359 to a little street called Adams Field Road to Wilson Road, then take a right on 362 to Morton, which will bring me back home.
Depending on your exact start point, it is just under 2 hours to ride it and around 75 miles.
Google maps link
Another road I like is FM331 off FM 529 just outside of Bellville. The north side of it turns into Oil Field Road, and is paved, but rough. That brings you up near Hempstead, but you can take Racoon Bend (turns into FM 1456) towards Buckhorn, then head north on FM 1371 which will bring you almost to Chapel Hill. You can ride 1155 North of Chapel Hill up to 105. Once there you can either turn right to head towards Navasota to ride FM 3090, or turn left to ride towards independance to ride 390. If you ride 3090, you can head back down towards Anderson and then ride 149 to Mongomery.
There are tons of roads in Austin, Grimes and Washington Counties that are great 4-8 hour rides.
Some of the funner roads I have ridden I found just by riding around and turning somewhere off the main roads. 390 was one I did not know about and just came across it one day.
Just curious, what bike you ride?
That road was a huge, fun surprise the first time I rode it. I never knew it was there till I was heading down it.