Actually it was just the original designers' idea for it to be two 25-story towers that straddled Boston Ave. As the story goes, John Williams looked at the model, picked up one of the towers and stacked it on top of the other and said, "let's do it like this instead" (Or something along those lines). So I don't think it was about the extra expense, I think it was just that he wanted one really tall building instead of two shorter ones.
Yeah, I was just going off what I read. You are probably closer to the truth and I was going off urban legend on Wiki
As for the windy days, I don't think it will be that big of a deal. I've worked on the upper floors of the BOK Tower for 15+ years. The building most certainly sways in the wind... you can see it often because the blinds will gently sway back and forth... on really windy days you can see the water in the toilet bowls moving a bit.
But in those ~15 years there has only been maybe 2-3 times that you could literally feel the building move; and it doesn't feel like you're on boat or something... it's just a very odd feeling... it's hard to describe really. I never felt sea-sick though, and I'm someone who will ALWAYS feel sea sick on a big boat.
I spent three months back in the mid 90's doing work in the tower on 43, 44 and 45 for Vintage petroleum, and noticed the slight movement from time to time. Before that in the 80's I worked for a courier company and spend a lot of time in several buildings downtown and where I noticed it most was in the freight elevator vestibules at the tower because you could hear the cables moving. The one building I seemed to notice it the most in is One Gas. It has according shaped panels in the expansion joints and you can hear them creak and kind of feel the movement.
My comment about the one for OKC was at the proposed height you would be way above Williams and even with the smaller profile the higher up the more movent that's noticeable. It was a tongue in cheek comment about need Dramamine.