Which is Faster? : Multi CPU Systems -vs- Single CPU Systems

As far as single CPU vs. Multi-CPU, it depends on what application you're running. For example, I have a Mac Pro with 8 cores (2 x 3.2 quads), and most apps don't run faster than they would with a single processor, just because they are not optimized for more than 2 cores usually.

It depends on the task you're performing to affect the speed for OS.

SSD is faster than drives in RAID 0, is faster than standard drives.

Of course there's a degree to the performance for cost ratio. I've got two 10k RPM drives in RAID 0, and it's fast enough for me without the premium of an SSD. It does, however, take up two of the hard drive bays on my Mac Pro, so that's the downside.

Going with a multicore CPU offers more performance for the money but a multi CPU system offers less performance for the money.

and avoid raid and get a SSD

have at least a fast 64GB+ SSD for the OS and installed apps, then a 1-2TB drive to store everything else. (it is faster than 2 high performance HDD's in a raid 0 and is more reliable)

If you have a ton of money, I recommend you go with a single CPU core i7 system

In order for multicore processors to be useful software must be written and designed for it. Typically modern operating systems contain technology that spread the load over the multiple cores this can provide a speed boast if running multiple applications as one single core is not doing everything. However creating software that supports multiprocessing is extremely difficult so individual applications are often not written for multicores and therefore a multicore processor isn't much faster when running single applications. As technology advances and our approaches towards writing multiprocessing applications changes a multicore processor would be much faster so much that a quad-core processor with each core running at 1ghz would be significantly faster then a 3ghz single-core.