[Steve]

I think I can safely say that all of the regular posters here still have mono in their setups.
Braid gets expensive, got too many reels to load up.
Yes, it does seem to cast farther than the same test in mono, not real far though.
I know that I won't have braid in the waterat night when there are Sharks around though, seems like they swim through and cut it more often than mono.
Braid also requires a better rinsing after the trip, because it's not smooth, it hangs onto more salt, sand, etc than mono. I have noticed a very tiny amount of feathering in my 35# braid that I used in FL, not nearly enough to trash it though.

I have 17 lb mono on my surf rigs, I really don't think you'll notice a difference in the toss between 17 and 20.
Always go with the lightest you can get away with. With a good amount of line and a properly set drag you shouldn't have any problems. Pulling the line straight down with the tip bending, drag should be set at 25-33% of the line test. A straight out pull should be set at 15%. I personally won't go below 17# on surf rigs because of line chaffing in the sand.

I really haven't noticed much difference in mono or braid diameter difference, not enough to make me decide on that factor alone when considering test in each type of line.
Braid's good, I'll keep both lines on my reels.