Need help in deciding dell workstation

Hi,

Here is my config

Base System Dell Precision(TM) Intel(R) Core(TM)2 Duo E8400 (3.0GHz) 525W
Operating System
Genuine Windows™ XP Professional SP3 (English)-Downgrade Vista®
Business 64-Bit
Chassis Orientation Minitower Orientation without 1394 Port edit
Dell(TM) 2007FP UltraSharp(TM) 20" Flat Panel LCD Monitor (Analog &
DVI)
Memory 4GB (2x2GB) 667MHz ECC Dual Channel DDR2 SDRAM Memory
Boot Hard Drive
(SATA/SAS)
160GB SATA HDD with 16MB Cache (3.0Gb/s, 10k RPM)
1 SATA HDD without RAID.
Video Card
512MB PCIe x16 nVidia Quadro FX1700, Dual DVI, Dual VGA-áand
DVI+VGA

I am thinking to change the FX1700 with ATI V5600 (as a conclusion from my other topic, that V5600 is much more better than FX1700 for use in UG NX). Is it compatible with the motherboard and processor I chose? Thanks

I think 4 gigs of ram is too much, so is it better to downgrade the ram and upgrade the processor instead?

My application is only for modeling, assy and drafting with avg 3000 parts (200 unique parts).

Thank you for your feedback.