Riverdale smacked MBA in a scrimmage this year (42-0). They've had our number the past two years in scrimmages (I think the '04 scrimmage result was 35-7). However, from 1999-2003, MBA "won" four of the five scrimmages, if not all.
Riverdale does have speed to burn, and defensively just swarms opposing offenses. Most of the points they give up is in mop-up duty. The 2004 edition of Riverdale went 10 straight games without giving up a TD (one safety and two FGs given up in that stretch).
I haven't seen St. X this year, but my guess is they'd give Riverdale a good game this year, and a X win wouldn't surprise me, but they'd have to make the most of any scoring chances. When MBA has had stout teams (Trinity fans saw a pretty good MBA team in 2003, but the 1999 and 2000 versions were even better) with hard-nosed defenses, they have handled Riverdale and their speed well, and I'd venture to say this year's version of St. X would be considered "stout", based on what I've read.