John - yes exactly - that's what I had in mind when I did the exercise - to get as comparable as the offerings allow.
Now the question this raises of course - triggered by Alan's comment and relevant to the OP's initial question - how much computer does one really need to get top-flight performance out of Lightroom or Photoshop? Is a 5000 dollar computer total overkill, in the sense that a 2200 dollar outfit would be just as fast and just as stable and just as robust? I ask - I honestly don't know - I think it's an important question. One can always take flight in safety by buying the absolute best because by definition it can't get any better, but how useful? You know what I mean - it conjures up the analogy of driving a Porsche in a 30 MPH speed zone.
It is interesting that Apple has the i7 chip in the iMac, which is a somewhat limited computer (i.e. very limited scalability and has experienced some technical glitches) but not in the MacPro. I'm wondering why. Do they think a Nehalem solution is better for the purposes of the MacPro, or it is just a matter of time before it too goes i7? Any thoughts on the merits of Nehalem versus i7?
The i7 vs Xeon (Nehalem) which are somewhat both of the same architecture, its Desktop vs Workstation. When comparing Macpro vs PC it has to be compared to a Workstation grade system, It can DIY, Dell, HP or IBM etc... The i7's are great little snappy computers, and can perform any task at hand quickly. However, its when we start to truly multitask that they start to struggle (how do we compare or measure this?) In true multitasking environment, you will see the workstations start to shine, they are slow out of the start blocks, but when they build momentum, they get the jobs done.
I don't currently have the latest computers, but I did some tests a few years ago with the then top of the range. I had a Dual Opteron workstation and I had a Intel Quadcore Extreeme (Desktop) both with 8gb of ram and sata hard drives. The Opteron had a Nvidia Quadro FX 3400 and the Desktop had a Geforce 7900GT. Cost the Workstation was between 2-3 times more expensive, but it only gave me 10% speed increase in my benchmark test, however, sitting and doing my work on either of these machines was a different story. The workstation was the most comfortable machine to work on, everything just seemed to be more smooth, running raw conversions, doing photoshop work, rendering a pano, being online, running backup etc...all the things that we do in a normal days work. The Desktop on the other hand, was great to start with, but as I added more and more applications on, as I progressed in my work, it started to sink into its knees. (i know this is not scientific but an opservation)
Some one in an Australian Photo magazine, made a comparison with the latest Macpro and the a new top of the line HP workstation. I think the HP was 4x the price of the Macpro, but it was twice as fast at converting raw files.
I think when you choose an OS, get what makes you feel the most comfortable. Sure there are many if not most photographer, who thinks that their images will look better if they are done on a Mac. A lot top photographers do use Mac's but are they good computer operators or are they great photographers?
I say, pick your sword of choice and prepare to have some fun making images. One computer may get you there sooner, but either of them does not make you more or less creative. Your choice of lens is a far more important topic.
all the best
PS: If i have gotten it wrong please correct me