I didn't apply to I/O programs, but did look at them. Take the following with a grain of salt since I don't know it as well as others may.
Importance of prestige depends on what kind of jobs you're looking at. Want to be in a top consulting firm? Definitely. Looking for a run-of-the-mill HR job? Less so. It matters some for academia as well, but the prestige of your advisor matters more.
For stats, its somewhat similar to clinical. GPA 3.5 or above. GRE 1200 or above, 1300 or above for top programs. You can get by with a little less research experience, but I think a year or so is still needed. They'll look more favorably on non-research jobs as well...the top candidates often have experience as an intern or employee in either a corporation or a consulting firm.
Like I said, not exactly my area, so take it with a grain of salt. Its a LITTLE less competitive than clinical, but not by much, and its becoming more competitive every year.