Should I Go With Apple's Ram ? Options

[Milca]

Hello guys
I have a question about RAM .
I’m purchasing the Mac dual 2.7 Ghz.I’m not sure whether I should go with apple’s RAM(1 gig – 250 $) or rather get minimum 512 Ghz which comes with G5 and then buy extra RAM somewhere else .
Don’t know if it’s truth but I’ve heard that I can get high – performance RAM for the same price I would pay for apple’s RAM.
So this is my first question – anybody has experience if other high – performance RAM can make difference comparing to apple’s RAM.
Second question is simple.
I’m gonna be running a lot of apps. Don’t want to name them all – but from platinum waves.native komplete 2 to BFD and most spectrasonics products.
I’m planning to get 3 gig of RAM total.I’m not sure if this is not too much.I’ve been advised that 1,5 – 2 Ghz should be enough and also on the other hand that there is never enough RAM ?
Thanks for your time.
Milan