There are two posters for the training room—"anatomy poster" and "brain anatomy poster"—both with the same attributes, most importantly "+1% training speed". The bonus stacks. Because unlocking costs 80 kudos do I even need the other one?
There is no reason for unlocking both, it's pure aesthetics.
By the way, if you are looking to optimize your training room, the encyclopedia bookshelf II offered by getting 2 stars in Mitton University gives you 4% per item, so you can get even more effective training using those instead of posters.