Well, big reason I went with HO 40 was because my car has a black interior. When it was all said and done, the tint looked waaaay darker than I expected. It's hard to tell until they put it on your car. The owner took a couple of films out of their boxes to show me the differences, and she showed me her car for a reference (she had a silver Merc). On her silver Merc with gray interior, her HO 40 looked pretty light. On my black on black 330i, it looks pretty dark. So if I had to do it again, I'd leave it the way it is.
The other thing is that I already think it's a bit difficult to see out of a HO 40 at night. Any darker and I'd feel pretty uncomfortable. One more thing, I'm not sure Song's has an HO 30. I can't remember, but for some reason, I thought it was HO 60, 40, or 20. By the way, Song's won't do your rear window with 20 I'm told, but I didn't have to worry about it since I got 40 anyway. You may want to ask them about it.
EDIT: oops, just realized you're in Florida! Hahaha...
