Building a New System - Use Onboard Video or Existing GeForce3 Video Card?

I am building a new system with the Epox 8RGA+, AMD XP 2500+ w/Barton
Core, 512 MB 3200 DDR ram (2 - 256MB sticks which will give me the
dual channel feature) . I have a two year old 64MB ASUS GeForce 3 that
I have loved since it's install.

My question is: Would I get better performance assigning 64 or 128MB
of my 512 to the onboard GeForce 4MX part of the motherboard or should
I use my trusty old GeForce3 card?

Thanks for any input..
Rick