Interesting question, and I like to think of it this way;
An 8wt line is probably made for all 8 weight rods, slow, medium, fast, and extra fast actions,
If that's so then they are probably all made for the medium action rods,
Therefore they may not have enough weight for the extra fast rod,
And I don't see the line companys making an 8 1/2 or an 8 3/4, etc. line sizes, so overlining or even underlining a rod makes a lot of sense. I really wish there was a 12 1/2 wt line for Tarpon.
I don't have as much of a problem with the line splashing as I do with the fish seeing the line in the air, the shadow it makes during the cast. And I don't think clear lines help this situation, they both seem to make about the same shadow.
But a very important consideration is in using tropical lines for tropical conditions. The soft coldwater lines I use for Steelhead just won't cut it here in Florida, even during the winter.
Good Luck Dave.