Number of cores vs processor speed vs RAM

This summer I am going to start editing 24P HD format digital video on Final Cut Studio 2

I can buy a 3.06 w 8 MB RAM 2.66 GHz iMac or a 4 core Mac Pro 2.66 Ghz w 12 MB RAM or an 8 core Mac Pro 2.66 with 16 GB RAM (I plan to choose the ATI Radeon 4870 graphics card with 512 VRAM)

My goal is to choose the hardware configuration from above that will provide the highest performance for editing video in Final Cut Studio 2. I am lost.

Which variable is most important for video editing: Processor speed? Amount of RAM? or number of cores? How do I weight the performance gain provided by each variable?

If pay all that money for 8 cores will end up have cores sitting idle during editing?

Might the 3.06 Ghz iMAc edit nearly as fast as a 4 core or 8 core Mac Pro?

Could someone with expertise in designing Mac hardware give me some advice?

Thanks


Brent

Final Cut appreciates the extra cores: Final Cut Studio 2 and 8-core Mac Pro

Gigahertz isn't a major issue - a few hundred megahertz here and there on the same processor class isn't noticeable most of the time.

8 Cores is very expensive though and the benefit probably isn't really worth the extra cash.

The iMac will be fine, but considering the fact you can't upgrade the GPU, which you might need to do in the future, I'd go for the 4 Core Pro to be honest.

i would say a real life example would be carrera 6. I can render, literally twice as fast on the mac pro with 4 cores vs. my new imac.

It's also important to remember that the iMac is basically a laptop with a desktop drive.

The CPU, ram bus etc are all pretty much mobile specs.

So, in the case of editing HD, the Mac Pro should prove a lot more powerful, plus you are likely to put a lot more ram in it.

FWIW, I see 2008 Mac Pro 2.8 8-way machines for $2250 or so. No iMac or Macbook Pro is going to be able to touch that performance.

Core utilization is on the software. Compressing tends to use multi cores well, other tasks like timeline editing and filters vary wildly. Some tasks may seem single threaded almost, ie like some Photoshop filters.

So - nearly on topic which is good for me - if one bought the standard 2.66ghz single i7 mac pro, could that cpu be upgraded easily? I wondered whether to buy the 1 or 2 cpu mac pro.