I'll just throw another 'pro' to the Vienna-in-IPA category. I did a 60/40, 2-Row/Vienna IPA last summer that was awesome - need to do that one again actually.
I do remember the boil looking like egg-drop soup from what I'm guessing were the proteins from the Vienna, so I just might try a step-mash next time. Even using US-O5, my beer ended up clear after 2-3 weeks in the keg, but couldn't hurt to get more of the proteins out early.