So is there a hardfast rule against the belt and vest combo? What's the reason behind separating the two? Is it simply because it gets to "busy"?

I tried reading through the Kilt Do's and Don'ts, but... wow, I can't tackle that right now.

Also, what level of formality would a vest and long tie (both tuxedo black) take the kilt? I have two summer weddings lined up to attend this year, and both brides have requested my presence avec kilt. One is here in St. Louis in June, so I'm not terribly worried about the weather, but the other is in South Carolina in the middle of July, and I don't want to bake, so I'm trying to figure out what to wear instead of the jacket.