The 4.5GHz Fritz results are 9.8% faster which doesn't help corroborate your initial claim of performance decrease? . . at least it seems your CPU crunches faster at the higher frequency which is your main concern . . . I'm not that familiar with Vantage CPU benchmark and therefore don't know if 500 points is a lot *or* a little!
A quick brute force explanation would be that lowering the LGA775 CPU multi from its default overclocks what you think is the FSB, although its actually called the NBCC (Northbridge Core Clock) which is in fact a processor called the Northbridge and acts in a similar way to how you understand a regular processor i.e higher frequency = faster . . . and the faster it gets the more volts (vNB) it needs and the hotter it runs . . .Can you explain that bit about the NBCC? Always looking to expand my knowledge
"A Veteran P45 Express Northbridge Chip with heatsink removed . . . . PIII Coppermine anyone?"
Most LGA775 clockers have a good enough understanding of what FSB does but few of them have the knowledge that the FSB you see in CPU-z really only relates to working out the Processor MHz and memory speed through the use of memory multipliers and doesn't really relate to the true system "Northbridge" frequency and the way that effects system bandwidth!
Using your E8400 as an example, lets say we set it at 9x400=3600MHz and I asked what is the FSB? . . . most people would say 400MHz which would be correct:
now lets say we lowered the CPU multi from [x9] to [x6] and again I asked what is the FSB? . . . most people would say 400MHz which would be incorrect? . . . . the correct answer would be 600MHz
In the two examples given above we have *increased* the Bus Bandwidth from 12.5GB/s to 18.75GB/s which is a mighty 50% gain just by lowering the CPU multi!
To work the NBCC speed out you take the native CPU multi and divide it by the set CPU multi, you then take the resulting figure and multiply it by the set FSB to work out what is the actual NBCC frequency . . . using the two E8400 examples above:
- 9/9=1
- 1x400=400 MHz-NBCC
- 9/6=1.5
- 1.5x400=600 MHz-NBCC
NBCC MHz determines the speed of the data transfers between the CPU and the System Memory so its worth understanding if you want maximum performance, most advanced LGA775 tweakers will also *not* run their memory [1:1] sync and instead use a Memory-Multiplier along with a more conservative set FSB and a knowledge of NBCC and tRD (aka Performance Level) to speed up the data transfers!
To sum up, on the LGA775 platform factor in a lower CPU multi combined with an upward memory divider for best performance!
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. . . at least I can't prove it either way but I ran several LGA775 chips over the course of a few years and never ran into this issue myself . . . having said that I did experience symptoms on a system that made me think that perhaps the chip had weakened . . . funnily enough that was also an E8400 that I was trying to get to 4.5GHz but couldn't get it fully Prime stable so gave up and backed it down to 4.25GHz which had previously run fine but after spending a week or two running it at 4.5GHz with heaps of vCore I could no longer get the system stable! 
