How much bang for the buck between a Xeon 3.0 800FSB and a Xeon 3.0 400FSB??

I was wondering if someone could give me an opinion (or if you have the
benchmarks ).

I'm thinking about upgrading to a new Dell Precision WorkStation 670 - Intel
Xeon processors up to 3.00GHz with 1MB L2 cache (Dual Capable) 800MHz front
side bus and Intel Extended Memory 64 Technology and dual-channel DDR2
400MHz SDRAM memory. I currently have a Dell Precision WorkStation 530 MT
with a 1.47 gigahertz Intel Xeon(Intel 860 Colusa Chipset), 8 kilobyte
primary memory cache, 256 kilobyte secondary memory cache and Rambus RDRAM
running at 400mhz.

So my question is how much of a performance difference would I see between
the old Dell 530 and a new 670 if I were to upgrade my current processor to
a PENTIUM 4 XEON 3.0GHz FCBGA 400MHz 512K CACHE???

Thanks in advance.
CES