FSB vs. CPU speed - why the rush for higher FSB?

[Chike]

This is a an educational question by it's nature.

I ask this because I see many people pushing their FSB up while compromising CPU speed.
There are several reasons I can understand for doing so:
a. The CPU cannot overclock above certain speed.
b. The CPU cooling is exhusted, or you just want lower CPU temperatures.
c. You want to run at highest FSB possible.

For the first two reason you would (possibly) get higher memory bandwidth and lower latencies which some application would benefit from. The third, while not being rational, is still acceptable.

But does it make sence to have a lower seepd and higher FSB for practical reasons?
If you have a CPU that is capable of doing 4.5GHz with 450FSB is there any practical reason to run it at 4.25GHz with 500FSB, other than those mentioned above?
Would benchmarks (ther than memory benchmarks) show any gain, and what benchmarks if there are?

[sotti]

Re: FSB vs. CPU speed - why the rush for higher FSB?

I played around with this with my opteron X2,

I found for 99% of what I cpu speed > *

[Psycho101]

Re: FSB vs. CPU speed - why the rush for higher FSB?

There don't seem to be many gimping CPU speed over FSB, rather they're finding the max FSB within the range of max CPU.

Good benchmarks that care about FSB include the usual RAM tests, plus things like SuperPI.

Anything else that heavily relies on the FSB will benefit, including but not limited to video encoding/transcoding, audio work, encryption, compression/decompression and also some real world apps and games.

As always, test your config. If getting 425*8 vs 400*8.5, the higher FSB would be better. Choosing 425*8 over 400*9 though, would likely be counter productive.

As D-an-W, grishkafool and BoombasticSloth have done, maxing CPU vs FSB to within ~100MHz of max CPU speed is best. I'm sure they've all tried for the highest FSB they can, but not for 24/7 I'd imagine, just for kicks.

In your case, 420*8 may give slightly better performance, but only if you can run the RAM at a similar speed. Some FSB's take you out of range of ideal RAM multi settings which means that even a higher FSB and CPU clock can perform poorer in some cases.