Iran would defeat Saudi in a couple of Days at worst.....so long as the Western Powers stayed the heck out of it.
That, alas, shall not happen as that would give the Iranians full control of the Persian Gulf and a huge amount of Oil (not so much the Oil itself but the Revenue it brings in on the World Market).
As they are a bit belligerent of late....if they had control....would they become far more willing to deal in a more acceptable manner with the Western Powers?