Coming late since I missed this thread earlier - I'm most of the way through a PhD in medical research/biology and most of my peers are bright-normal, not a ton of people who approach genius level (although there are a few exceptional people, like in most educated fields). I don't know anyone's IQ of course (or my own) but I'd guess most are in the 1-2 SD above normal range, so a fairly bright crew but nothing too crazy, and I doubt I'd be able to pick someone of average IQ apart from the others. The people who do best tend to be the ones who are hard working, persistent, patient, and logical in the sense that they can design experiments effectively to answer the questions they've come up with (hopefully useful questions). The clearly super clever ones do well too but only if they're good at following through with all their crazy ideas.
The people who struggle most are the ones who don't seem to understand scientific thinking (why do we do things certain ways?) or similarly, can't get the hang of designing/carrying out experiments i.e. you don't just do arbitrary experiments because that's how the last person did it! think what do we want to learn - what's the hypothesis? what do we need to do to test this hypothesis, while using reliable techniques and good controls, to get results we can trust? It's not so much straight IQ as it is a way of thinking; most people drawn to science tend to come naturally to that way of thinking, but those who don't can have trouble. Psych is a bit different from hard science, but probably a lot of these things still apply if you're doing experimental psych.
edit: oh yeah and also writing skills are incredibly important overall, and a major contributor towards success as measured by publications.
From what I know of you @Glycerine I don't think you'd have any problems at all as far as intelligence goes. It's hard to know without actually doing it how well you'll do in research anyway, and more importantly how much you'll like it - that's what the Masters is for.