If I'm not mistaken, China is the single largest buyer or Iranian oil. Sanctions have meant all but a dozen or two states are customers. Slowing (or temporarily stopping) flow through the SoH would obviously affect other exporters, and would push the price at the pump way up, but it's not a free play for them (Iran). They'll suffer for it as well, if not more than others. I'm NOT suggesting they wouldn't do it, but it wouldn't necessarily be in their interest unless they were looking to buy time and a modicum of leverage to get back to the negotiating table - which also will probably not go well for them.