Upload & Sell: On
Aubsxc (and Bif),
I'm certainly not going to defend Apple's record for powerful desktop workstations because basically it sux. Somewhere probably about 3 years ago, Apple decided it was a consumer goods company (remember they dropped the Computer from their name) focused on iPod, iPhone, iPad, iWatch, iShoe, iAnything they can think of. The market has certainly rewarded them. They still make excellent laptops (I'd argue the best) and the iMac is all the machine that most people - including a lot of creative people - will ever need. I recently set up a top of the line i7 27" iMac for my significant other and was impressed that in most ways it out performs my 3-year old Mac Pro. Like many others I was underwhelmed when the specs for the nMP were released.
I was offering and discussing used machines in response to the OP's original question of how to set up for PP. We wandered off into a critique of Apple's high-end (snicker) hardware. As I see it the OP and really all of us are balancing three things: price, performance, and assured reliability. (One could also label this as a measure of how risk adverse one is.) As any student of statistics will tell you, "You can't optimize all the variables in any multivariable equation."
I've certainly built my share of FrankenBoxes including a couple of Hacintoshs back in the day when one had to "find" a boot ROM thru what might be termed dubious means. I haven't paid attention to that whole world in some time, but I suspect since the move to Intel chips a Hackintosh has gotten a lot easier to build.
As I see it if the OP wants maximum reliability buy new from Apple get AppleCare and if he/she is in the USA they have about as reliable computer as is currently available on the market. This is of course the most expensive route. If one is willing to take greater risk, then used machines become a choice and again one can get a better price off of eBay than from a competent used dealer which - despite Bif's screed on the subject - do exist. Finally there is the roll your own option. It's commonly said you can get better performance than Apple's offerings at half the price. This is true if one only counts component costs and doesn't value one's labor. At this end of the spectrum you have the best performance, good value, but the highest risk. Anything that goes wrong and you are working without a net.
There are many - I'd say most - users that just don't have the interest, time, confidence, experience, whatever to build their own box thus this isn't really an option for them. Me? I stopped hacking hardware a while back in favor of other things like more photography. I do admit that my old "I can roll one better than yours" has popped up, but I'm trying to ignore it for now.
I really don't disagree with any of the criticism leveled at Apple. You should see my list which I regularly send them and the regularly ignore. I did want the OP to understand that there are a number of levels from which to choose. If one has the money and doesn't need an open box to add functionality, the new high end iMacs are quite nice - but of course cost more that building one for yourself.