Ohio River
I worried about the same thing before I towed my Catalina 25 to it's new home on the Ohio.We only got in a few weekend sails last fall before flood season started but it wasn't as bad as I expected. As mentioned before, keep your head on a pivot (check 6) and watch for floating debri. My experience was that I could make decent time upriver on a broad reach. With the wind behind it was a bit slower obviously. With the wind running with the current it becomes a tacking match but is still doable. It's just more work. Now I don't have any fancy instruments to tell me about wind and speed so I can't tell you what speed we were making on any particular point of sail. I will say that as opposed to open ocean sailing, with river sailing it is pretty easy to track your progress or lack thereof.