[Dream] Quad core or "just" Dual core?

[spork]

I'm in the process of deciding what my next system should be, and I
came across AMD's supposedly hottest processor - Athlon 64 FX. I
understand that this is a quad-core thingy, and it seems to be amongst
the top five or so on most of the benchmark tests at Tom's Hardware:
http://www23.tomshardware.com/cpu.html
Best of all is that it's clocked at 3.0 gHz, and, if I've understood
things correctly, this means that *one* core is as good as my current
PC.

Intel's dual core processors seem to average slightly higher, but they
cost, like, twice as much. Anyway: Should I even bother going
quad-core? I use my computer for music production, and don't run more
than two (rewired) apps simultaneously, so I'm not really much of a
multitasker. I would like a system that can get me *settled* (for a
while, anyway) - I hate upgrading (well - the part which involves
reinstalling and moving all your junk from the old computer) I
currently have a P4 3.4 gHz, and I'm starting to push it. I'd be
delighted if someone in the know can tell me that an Athlon 64 X2
5600+ (2.8 gHz) will a) kick my current processor's arse, and b) be a
good choice for the future. (Partly because the store I'll order my
system from doesn't have the 64 FX's in store.)

As for RAM: Do I really need more than 2048 GB?

Are there other factors that I need to take into consideration for
performance? I'm thinking about this graphics card from Sapphire
(because it is cheaper than many others, and has two DVI plugs - in
case I want to use two monitors) There is a lot of fancy details here,
but it's all Greek to me:
http://www.sapphiretech.com/us/products/products_overview.php?gpid=162&grp=3


And nobody needs to bother suggesting Apple. I am aware of that
particular company.

/spork