Upgrading my machine.. memory question

I am a long time system builder and have built my last 5 machines..

Current Hardware:
3.4Ghz P4 800 mhz FSB
925X Intel Mobo
3 Gb's DDR2 533 Mhz
EVGA 6800 Ultra Video Card

Upgrading to:
Conroe E6600 2.4Ghz 1066 mhz FSB
P965LTCK Intel Mobo
EVGA 8800 Ultra Video Card

My question is regarding the memory....

I know my existing 3 Gb's of DDR2 533 mhz memory will work with this system.

I just want to know how much performance I would gain by upgrading to 800 Mhz memory.

I read a little tid bit on Intel's website about how the P965 chipset gains performance from 800 mhz memory.

I have always related system FSB with memory speed. So 1066 mhz FSB /2 = 533Mhz memory. 533mhz X 2 - 1066 mhz FSB.

I have spent prolly $400.00 on this memory and currently do not see any reason to update it.

What are the advantages to using 800mhz memory? or is this just a marketing ploy.

THX