Which mac pro configuration - how many can be effectively used

Question

Hi all
Well, this question has been asked many times before - and I've read the macperformanceguide.com articles - but I can't find any info relating to 2010 Mac Pros or my typical usage. So any advice/links greatly appreciated.
I'll be investing in a Mac Pro soon and really need some solid advice on whether the Quad Core 2.8 Ghz (12Gb ram), Quad Core 3.2Ghz (12 Gb ram) or 8 core 2.4 Ghz (6Gb ram, upgrading later) will be best for my needs.
Typical usage for web design on my Macbook Pro is currently the following running/open at the same time: Wacom tablet driver, time machine, billings, mamp, 2/3 browsers for testing, vmware fusion running windows xp, emails, dreamweaver, smultron/textwrangler, fireworks, photoshop, fontexplorer pro, terminal and gitx, Skype - they all end up open while I'm messing about with files, talking to sub contractors, etc. Any I may well end up with Numbers, Pages, etc open as well. My Macbook Pro (4Gb ram) is ageing and just can't handle everything quickly.
I'm looking for the best system for now and 3 years down the line. I know a lot of software still doesn't make use of multiple cores so the quad cores would seem to be initially a better bet with their faster clock speeds. But I don't know if OS X will automatically allocate threads from different software to different cores - in which case 8 cores would help with the amount of software I'm using at the same time.
Thinking about 3 years from now the 8 core allows me to add more memory but - will the extra investment in the 8 core now provide a real benefit in 2-3 years or will the extra ram potential advantage be negated by heavier, hungrier software requiring faster speeds from other parts of the system.
Which ever system I get, I'll be adding extra hard drives over time, maybe upgrading the graphics card if that becomes necessary. It really comes down to the number of cpus, those extra cores and the extra ram possibilities.
Thanks in advance for any help!

Answer 1

Taking Applications that are inherently single-threaded and running them on multiple processors is a Classic unsolved problem in Computer Science. This means that Applications will only speed up when they are Hand-coded to run speedily on multiple processors. Although the latest version of Photoshop is Finally seeing this treatment, many more mundane Applications will never be done this way.
As long as it remains so (which is likely to be permanently) MegaHertz (processor speed) matters, and once you have a handful of processors MegaHertz matters a lot more than number of processors.
Your list of prospective Mac Pros does not include the Mac you should be considering first, the 6-core 3.33 GHz Westmere, available as a build-to-order option of the four-core mac Pros. It gives you the fastest clock speed of any, and its Hyper-Threading give you 12 effective processing units.
The premium price of an eight-core or 12-core is so large that you could buy another complete Mac Pro for the same price, and use them separately or as a compute-farm.
If you are handy, larger DIMMs (8GB each) are available from reputable third party memory suppliers, and they stand by their correct operation in your Mac with one caveat: They do not play nice with other sizes mixed in. So if you are contemplating large memory size, choose 8GB DIMMs from the start.
Three DIMMs is optimum, but studies are showing that the penalty for running with two DIMMs or four DIMMs is under 5 percent in real-world Applications. So starting with two 8GB DIMMS seems like a good way to go.
With this kind of large compute power, the remaining bottleneck quickly becomes Disk I/O. You should set aside a Boot Drive: a small, very fast Drive that holds only System. Library. Applications, and hidden Unix files including Paging. Users files should be moved to another drive to reduce competition for the Boot Drive. A small VelociRaptor works well for this. A small SSD is even faster.