About creating VM

Hi folks,

Host - Fedora 12 64 bit
KVM
AMD 64 Phenom II X4 955
VM - debian-503-amd64

I’m prepared running following command to install VM virt-install --connect qemu:///system -n vm10 -r 512 --vcpus=2 -f ~/vm10.qcow2 -s 12 -c ~/debian-503-amd64-netinst.iso --vnc --noautoconsole --os-type linux --os-variant debianlenny --accelerate --network=bridge:br0 --hvm

Shall I use: --vcpus=2

OR
–vcpus=4
???

This is a quadcore box. TIA

B.R.
satimis