I just bought new carpet and some dynamat for my EF, but immediately regretted lashing out as Falcons etc already have their floor covered in bitumen from the factory for sound deadening. Wouldn't I be wasting my time basically putting the same s**t over wahts alredy there? I was thinking of covering the doors maybe. Has anyone used Dynamat on their car before & was there any noticeable difference in road noise? etc. thanks..

Use it in the doors, the roof, the trans tunnel, anywhere theres bare metal. road noise doesn't come from the road it comes from the car resonating at many different frequencies as it travels along it. I done my au and I think the results are great, but the rule of diminishing returns applies. You could spend alot of money chasing all the noises.
Do you want to make you're stereo sound better or make the cab quieter ? Making the cab quieter you can just focus on the cars outer skins. For making the stereo better theres really no limit to where you can put it but best to focus on inner skins around speakers, after the outer skins.
Best thing to do is start with the largest flattest panels and work from there. The roof is a good one being such a large flat area works like a drum, but it's probably the hardest thing to do. Next would be door panels, pay attention to placing it behind any door mounted speakers. Then perhaps the rear parcel shelf then fill in the gaps in the floor.

Either way it will sound better! Can't go wrong with dynamat.

thanks mate. It's just for the road noise, i'll do the doors and parts of the floor that are'nt alrady covered from the factory.

Apparently a good thing to reduce road noise is to get underbody sound deadener (the paint on type) and do inside your rear wheel arches.
A lot of noise enters the cabin from there.