We went with Enterprise, and actually had our first call this morning with the Magento team about integrating with Marketo. It seems like although they are Marketo users themselves, they haven't had a lot of experience actually connecting the two platforms. They were, however, pretty confident about their ability to at least sync up an email opt-in within Magento that would sync to Marketo. Ultimately I'd like to get a little bit tighter integration than that set up, but it's a start.