Is in that a conspicuous difference between DDR2 SDRAM 667Mhz and DDR2 SDRAM 800Mhz when both run on 1066FSB?

Is within a noticeable difference between DDR2 SDRAM 667Mhz and DDR2 SDRAM 800Mhz when both are running on 1066FSB? Thanks!

Is in that a conspicuous difference between DDR2 SDRAM 667Mhz and DDR2 SDRAM 800Mhz when both run on 1066FSB?

No. (in other words logically there will be differences but I can assure you that you won't perceive them).
agreed with above poster. Though you will particularly want higher memory speeds, such as 800mhz, for overclocking...
contained by theory yes comparatively a bit. now surrounded by the real world. probobley not that much I don`t know 1-3FPS more in a video activity if that at all. the DDR800 have a higer Bandwidth then the 667. If i be you i'd still just buy the faster memory. it may not comfort that much now. but a couple years down the road that 800 will give a hand you alot more then that 667 if you upgrade. :)
depending on what you use it for yes. If you use memory intesive apps, you'll sense a difference. If you're just a unattached gamer and internet surfer, no.