Martin,
I was in Europe for xmas and found that Visa was accepted nearly everywhere and I didn't notice any O/S transaction fees on my monthly statement.
I did notice though that the exchange rate was not the best on my VISA purchases but it didn't matter much as I had already saved money by not buying travellers cheques.
If you take cash the Aussie $ is best, you also get better exchange rates for cash than travellers cheques. Shop around as exchange rates vary between banks.
When you run out o cash you can always withdraw cash from an ATM.
Cheers