Aussie SRT8 owner

Hi everyone,
My name is Matt. I live in Canberra, Australia. I purchased my 09 Jeep GC SRT8 in April 2010 with 4000km on it. I don't have to tell you what a weapon this thing is, it even surprised me. I drive high performance Holden SS and Ford XR6 turbos and Ford XR8's in the course of my employment so I needed something special to entertain me on my days off. Having previously owned Porsche, Audi, Range Rover, I was pretty hard to impress until I purchased my SRT8 sight unseen. The GCSRT8's are really rare over here (I have seen 2 others in nearly 2 years) as they are AUD$100k brand new and no one knows much about them.
Like any vehicle you have for a while, I am now ready to squeeze a few more kw out of the beast. I have no idea what to do to it, where to source the performance parts from or how much I should be spending. As you could imagine, the parts here are rare and expensive.
I have been told that a diablo tuner and cold air intake is a good start to gain 40 hp. Is there any difference in the output between say a mopar CAI, a K&N CAI and one of the American made ones that are a tenth of the price.
I currently achieve 0-100km/hr in 4.9 seconds. Is this standard and if so, I want more.
This is my first forum involvement. Great to hear from other Aussies and international friends.
Cheers
Matt