I've tried the fan blowing/sucking on the XP120, with a 68 cfm fan both cpu and mb temps improved significantly with the air being sucked up through the hs. With my YS Tech 128cfm fan I saw no noticable change in cpu temps, but my mb temps still improved. I think it will also vary based on your case config and air flow.

Bottom line is I've been using my XP120 with it sucking up throught the hs for some time now.