How much Ram is too much? + drive performance questions

[BusyBoxSt7]

I'm wondering a few things.

1) RAM
I know there's a huge difference between 1 and 2GB ram. I've got 3 right now. I'm wondering if I'll notice much better performance if I keep adding RAM and if so, how much should I do? .. Please note my use of HD includes VERY little TDM plugs, almost entirely RTAS.
2) Hard Drives
I've been shopping drives and noticed there are quiet/cool/energy efficient drives like the WD caviar green, and then noisier/hot/etc drives like caviar black... Is it necessary/useful to get a super high performance drive for the dedicated system drive? Project drives? (my guess is more likely a deal for the system drive but who has experience that can tell me?)

MY SYSTEM
Mac Pro Quad 2.66 OSX 10.4.8 (delaying Leopard due to PT8 upgrade fees)
3 GB ram
internal drives= 230GB system, 500 system mirror + personal, 1TB projects
external = 2TB WD enclosure running in mirror w/ itself (1TB.. it's a 2 disc enclosure)
PT HD 7.3.1
HD1 accel pcie (rarely use TDM plugs)
Lynx Aurora16 ADDA
UAD2 Quad almost omni (runs as RTAS of course)
hopefully some outboard and a console soon..