actualy the current set has best coverage it could ask for.
If he has something insane like meteor then we might consider otherwise, the current slidequake is better
Iron Head doesn't take away from Slide/Quake.
It would just be better than Return for the greater power, flinch while having similar netural coverage due to EQ/Rock Slide covering the resists.
Anyway, it doesn't have the option, so I won't go on about hypotheticals.
But if it ever gets a tutor, Iron Head goes on my Doryuuzu.