Atlatl Jones
Explorer
I agree. The feat's probably too good even with just +Str, and +(2xStr) is ridiculous. The same goes for the Iron Vanguard's ability.But I don't think you can apply the feat twice for one attack. That would be like getting twice the damage from "Astral Fire" if you use a power that has both the Radiant and Fire keywords.
Why not just be a barbarian, and take the at-will power that lets you push a target even when you're using a two-handed weapon. Then use a reach weapon and take polearm gamble. While you're at it, take the daily rage that lets you automatically knock prone one target per round, and/or the rage that lets you knock prone every target you hit.Don't forget to multiclass as barbarian so you're adding another +con mod with a daily stance (or possibly rage, don't remember for sure).
Then at 21st level, take Knock-Back Swing, which when you get an OA automatically pushes the target of the OA one square, even if the OA misses! With your combo of feats, that'll push all OA targets two squares and knock them prone.