I think 8/6/8 in anything oversize is really heavy. I'm willing to live with an occasional dent. But if you are using a high strength steel, dents are a lot less likely. Is the bike going to spend much time in a bike rack at work? If no, I wouldn't worry about it. I commuted on my Spirit for Lugs bike, but it didn't sit in the rack at all. People ride aluminum bikes with thin tubes and put them in bike racks all the time and I don't see much obvious damage.
Flop is annoying when you stand up, especially at very low speeds. Otherwise, it's not really noticeable. You can learn to live with just about anything.