That's an older chipset--is it within your budget to purchase a Nehalem-based system? Besides a generally faster architecture, you get faster DDR3 RAM.
Dual CPUs won't come into play much for modeling, just for rendering. I'd also look into purchasing at least 8GB of RAM (dual channel) or 6/12GB (triple channel) depending on which chipset you go with. It can really make the difference in complex renders.
Depending on the applications you're using, you might also want a higher spec video card or even a workstation card, again budget allowing.
1 x Intel Core i7 920 Quad Core Processor LGA1366 2.66GHZ Bloomfield 8MB LGA1366 4.8GT/S
1 x Please Use The Heatsink Included with My CPU -NOT Available with OEM Processors
1 x ASUS P6T X58 ATX LGA1366 DDR3 3PCI-E16 PCI-E1 2PCI CrossFire SLI SATA2 GBLAN Motherboard
1 x Corsair XMS3 TR3X6G1333C9 6GB DDR3 3X2GB DDR3-1333 CL 9-9-9-24 Core i7 Memory Kit
1 x Radeon HD 5870 850MHZ 1GB GDDR5 4.8GHZ PCI-E 2XDVI HDMI Display Port
This video card is available only as part of a pre-build NCIX PC system.
1 x Antec P183 ATX Tower Case Black 11 Drive Bay 4X5.25 1X3.5 6X3.5INT No PS Front USB & Sound
1 x Corsair TX750W 750W ATX 12V 60A 24PIN ATX Power Supply Active PFC 140MM Fan
1 x Microsoft Office Ready 2007 SP1 60 Day Trial - Free with New NCIX or Nx Fusion PC Purchase
1 x Seagate Barracuda 7200.12 1TB SATA2 3.5IN 8.5MS 7200RPM 32MB Hard Drive OEM *3YR MFR Warranty*
1 x Samsung SH-S223B/BEBE 22X DVD+-RW SATA DVD Writer Black OEM
1 x Logitech MX518 Gaming Grade Optical Mouse 1600DPI USB SILVER-BLACK
1 x Please Use The Onboard Sound Card Integrated On My Motherboard
1 x Please Use The Onboard Network Ethernet Card Integrated On My Motherboard
This is $1729 and the machine I am probably getting pretty soon. I will be using it for rendering as well but mostly for Lightroom/Photoshop. It's also going to be my main everyday computer with some gaming.