I'll be very candid and say that I failed both STEPs once each, and ended up at an AMAZING program that I'm extremely happy with. At the same time, it did prevent me from gaining interviews at places which I believe otherwise would have talked to me, such as Harvard Longwood and UPenn. Low scores are not fatal, but realize that there are competetive spots even in Psychiatry and you may close some of those doors if it is ivy/Top 5 that you absolutely have to have.