The dual 2.0 GHz with 8 Dimm slots, 8 X SuperDrive and PCI-X is the 2004 "Rev B" 2.0. This is actually your better machine and uses the PRO motherboard. 🙂
It is far better suited for PRO applications. Model#VPN-M9455LL/A
You should be able to fine one NEW for $1899 or less at most Apple
resellers or for $1649 Refurbished through the Apple Store Red tag sales.
The 2.0 GHz with 4 Dimm slots and 16X superdrive is the new 2005 Rev C
and uses the "prosumer" motherboard and standard PCI slots.🙁
Dual layer optical drives are cheap and easy to replace any time.
Otherwise you're spending $2299 for the new 2005 2.3 GHz model to get the best of the Rev B 2.0 and other BTO options factory installed.
The 'Rev B" 2.0 is like getting one of the last pre-smog control 67 Mustangs
where the Rev C 2.0 is choking on the EPA controls, but has a better stereo.