The extra 6" certainly wouldn't hurt, especially if you're planning to keep some larger species such as frontosa. For the species you listed, I think the 125 would work out well. The problem you'll most likely run into is actually finding a 180 on CL. There are a few out there, they just come up a lot less than the likes of a 125. I was looking for a 180 and ended up with a 125 and a 150 instead. I'm going to use the 125 for Tangs. If you do come across a 180 though, I'd definitely snatch it up.
Always verify tank dimensions too. I had 3-4 people claim they had a 180 only to turn out to be a 125 or similar.