eBay Australia doesn't really need to compete for sellers, eBay US does, and in shows a bit when you do comparisons like that. Pros and cons are really something only you can weigh up, but here's some things people don't always think of at first, that I'd personally put under 'con'. 

If you list on eBay US, you have to ship to the US, all of your prices must be in USD, and you will be paying conversion fees to get it changed to AUD. (This will affect your accounting - you will probably need to do it daily so that you can ensure exchange rate fluctuations don't put your figures out, or use some software that can do it for you - you can keep a PayPal balance in USD and only convert when necessary, but also keep in mind that before the end of the year, eBay will be managing payments and I haven't seen any info yet about listing on another country's site and currency, but needing payments to go into your bank account in a different currency).