Saudi Arabia and Iran are already in a state of undeclared war through proxies in Syria, Iraq and Yemen.
Iranians would wipe the floor with the Saudis - despite billions of latest US hardware regular Saudi army cannot handle a bunch of literally barefoot goat shepherds that are the Houthis in Yemen.
There was even a Shiite rebellion in Saudi Arabia (SA has a Shiite minority they're trying to pretty much exterminate) which routed the regular Saudi Army so they had to resort to massive air strikes to quell a domestic revolt. Pretty much left out of the mainstream news.
Iranians are itching to kill off all Salafis in SA but they cannot do it due to Western backing for the Saudi regime.
There are fascinating back-and-forth feuds on Twitter in which the Saudis threaten Iranians with ISIS and Iranians threaten back they'll raze the entire Saudi Arabia to the ground expect Mecca and Medina.
That's why Saudis rely on US protection - in Iran, especially in Revolutionary Guards propaganda discourses the US armed forces are often referred as "Saudi infantry" to illustrate, in their opinion, US subservience to Saudi interests.
Therefore, the Saudis don't want to fight anyone directly, they'd rather do it through their proxies like AQ, ISIS and JaT or by paying 100 billions dollars for someone else to do their bidding. Khm, khm.
Turkey has got a fine army but at the moment they're not looking of starting a war with Iran. They want to finish off the Kurds first.