You know, i got almost the exact same letter from the U.S Aussie embassy, except they quote 4-6 months for a family/spouse visa.
I completly agree that it's though waiting around but, they even say in the letter that there is a chance it will take less time..... i have just been staying positive by keeping that in mind.
Are you doing your police checks and medicals? I updated my CO when i first got the letter as to what was going on with that and got a response within 24 hours. I'm going to write to him again to update him--last time i didnt get any indication as to how my application was going....but who knows, might be able to get something out of him =)