1. Iraqi oil production now is slightly above pre-war levels (stable since December). Under the status quo, then, supply would not have increased much due to continued sanctions against the regime.

2. As possible counterpoints: With no war in Iraq, the US would have far greater capacity to mount a war against Iran. The American public would also have learned fewer lessons about the limits of US military power.

I think the major factor you'd have while holding as many conditions constant as possible would be the risk premium in the market related to Iraqi production, and the decline of the dollar. The Iraq war has cost around 540 billion US dollars, to date (ticker 1, ticker 2). The foregone revenue of Bush' tax cuts, by comparison, would be around 1.6 trillion US dollars (cbpp, rough projection on my part).

So, the war has clearly been significant in terms of its requirements for the money press.