I have a Corei7-950 with 12GB of triple channel Ram.
I just love it, it's mega fast. But i totally agree with Daniel here.
After upgrading to an OCZ Vertex SSD, i really noticed a huge performance improvement (logging in in Windows Vista x64 in 5 seconds!).
So best advice i could give, go for Core i7-920 and an SSD disk.
If money's not an issue, go for i950 and overclock to 4Ghz and go for a SSD Disk.
I get 213MB/s read speed of the Vertex disk. I love OCZ (first to implement TRIM command in their drives/firmware!). Under Win7 the SSD is recognized and it's tuned for performance (by turning of indexing services etc). Under Vista or older, you have to tweak it yourself.
Plus you can run Wiper.exe from OCZ once a month to prevent performance degradation.
This utility sends the TRIM command to the drive when you start it. Takes around a minute to run and it cleans all the memory pages marked as "to be deleted" so that performance is back up again in the 200MB+ a second range ;-)
I didn't fail !
I just found out 10,000 ways that didn't work.