(Breathing life into an old thread...)
I believe Merion has 7 holes between 350 and 410: #s 1, 7, 8, 11, 12, 14, and 15, and they are certainly the best set of medium-length par-4s I've seen (haven't played Pine Valley). Great bunker placement, some scary greens (esp. #s 12 & 15), the opening tee shot, the blind tee shot and the creek on #11, the stop-it-quick 8th green, and a couple of uncomfortable tee shots (#s 14 & 15). #7 plays shorter than its yardage, but I wouldn't put it in the driveable category. Placement over power to be sure. Even after good tee shots, a player could have wedges or short irons into all of these holes and still play them well over par.