I don't think either country has the wealth or the infrastructure to be able to manage any kind of war.
The Iranians fought Iraq for eight years. Most of those years, they were trying to invade Iraq, a country one third their size sitting in a flood plain. They lacked the infrastructure and logistical capacity for anything more than relatively static trench warfare a few dozen miles from their borders.
We've seen Saudi Arabia's military in action lately, intervening in Yemen, and it's been astonishingly underwhelming.
Both of these countries have failed utterly at any kind of massive power projection. The reality is that war is an incredibly expensive undertaking, and it goes through money and supplies at an astonishing rate. Having an army is one thing. Having an army that can fight on large scale operations is another. Having an army which can operate out of country and be maintained and supplied constantly is incredibly difficult.
I think that it always has been, but as mechanisation has taken over - as you need gas for vehicles, spare parts for vehicles, trucks, all kinds of, kitchens, food supplies, massive quantities of ammo, latrines, medics, and in larger and larger numbers, it's been exorbitantly expensive, and not just expensive, difficult in unique ways. The countries that have done it, the countries that do it, have extremely sophisticated infrastructure, and literally centuries of accumulated experience and investment. You can't create that overnight.