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If I were buying today it would be an Origin Professional with 16gb of memory, SSD's with most any GPU on the market. Even their lowest configured model is better than the current Mac Pro. No, I'm not crazy about Windows but there is a point where the available hardware exceeds the value of the Mac OS.
With respect, this may be true for you....but it is not true for everyone - and certainly not true for me.
The vast majority of people, imho, rarely make the computers push past 50% of its processing capacity more than once or twice a day. Even for a professional system, it is waiting for the user to do something, to finish reading something, to make a decision. The exceptions would be gamers and people who render, of course.
I just took delivery of a 'new' 2010 refurbished Mac Pro. Not the most cutting edge hardware, but it had several compelling features.
1) It has a 3 year, one stop warranty. I won't be required to spend any extra money on this system for a minimum of 3 years. Other Windows PC have this too, but this feature eliminates home-built systems.
2) It runs all of my SW, without any licensing hassles (other than I had to 'deauthorize' two old installations before I could renew the license on the new machine.) I didn't have to go through any hassle of transferring any licenses from OS X to Windows.
3) I am heavily invested in SW that is only available for Macs. I recognize that there will be Windows equivalents, but I want to spend my time working and building up the garden, not climbing the learning curves of multiple SW packages. I have a good workflow setup, and I can be very efficient pushing my work out the door.
4) In regards to the SW referenced in #3, I would need to invest in the Windows equivalents, which eats into any savings from the HW purchase.
5) My 4+ year old Mac Pro that I've just retired is still worth enough on the secondary market to subsidize the new Mac Pro by about 25% to 33% (on top of an already healthy refurb price discount.) In 3+ years I expect this new 'new' Mac Pro to also subsidize whatever replaces it.
6) Even if this 'new' Mac Pro is not cutting edge, it is still way way faster than old Mac Pro... but I only notice the speed difference 3 or 4 times a day. Usually I'm waiting for the internet, or I'm reading, or I'm waiting for a file to write to HDD. Or I'm thinking about what to do next.
For me, there was no question about sticking with OS X, hardware costs or not.