since we are kicking this horse again, here's what I ended up doing:
I had my old mac pro 1,1 on 10.6.8 for 7 years (actually my wife is still using it for video editing with Adobe Premiere and its still going strong). We got another apple 20" cinema display from somebody in our town for $100 too.
I looked at having a custom built Hack-pro, or going with a new trashcan mac pro, or a new iMac, or a new Mac Mini (btw - they severately hampered the expandability and power of the newest generation Mac Mini's so i am not convinced that is the way to go anymore) or getting something used.
during this process I discovered the 2 standard benchmarks that exist for computing power:
the geek bench single core and multi-core scores.
single core comparing things like web browser operation, or applications that don't support multi-cores (or virtual cores). Most intel processors have a "turbo-boost" function that accelerates the clock speed of a single core if the other cores aren't needed. Like the 2.66 ghz goes to just over 3 ghz in turbo boost mode. This helps to close the gap between Hack-pros or PCs with over clocked processors that might be running at 4 ghz or more. Obviously in single core tests these over clocked machines win.
multi-core comparing things like Photoshop and similar applications that utilize multiple cores and virtual cores. Although there are no audio applications used in these geek bench tests (as we seem to be the minority of power users, where most are doing video or especially photography) these multi-core tests let you see how a certain MAC is going to stack up against another for applications that use muti-threads / cores. Logic X takes advantage of 12 cores (24 virtual cores) now, and so does Pro Tools 11. You can see how using a lot of virtual instruments can really tax muti-threads using the CPU usage meters in both applications.
Its interesting to see what the multi-core scores are of machines like the current iMacs, Mac Mini's, 5,1 mac pros, the new 6,1 mac pros and compare the price you are going to pay for them. This site Everymac
http://www.everymac.com has a really comprehensive list of info for every Mac and might help you to separate the fact from the fiction.
Based partially on Everymac scores.......
I ended up buying a 12-core 2.66 ghz Mac Pro 5,1 on ebay with 32 GB ram, and 3 1 TB drives included. I then made a couple of upgrades in hard drives, and moved stuff over from my existing mac pro and just reconnected cables. Very quickly i was up and running again. With all the upgrades below I spent less than $2500 all in. Yes there is always a risk of buying used / older hardware in that things can go down, but with my previous Mac Pro experience I realized that they have pretty good reliability even being long after Applecare. Plus there is an Apple service center in town and they have parts available.
I have a 256 GB OWC Mercury Extreme pro SSD for the startup drive
A Sonnet Technologies Tempo SSD PCI drive mount with a 512 GB Samsung 840 Pro SSD on it (with space for one more SSD on the card so I can either add another and make a bigger faster RAID setup or have it run individually as a totally separate data stream) - about 60% full
a WD Caviar Black 1 TB drive for extra samples - less than 50% full
a couple extra HD's for audio record, client data, etc. and incremental backups of my client / personal data and audio record drive which run every 3 hrs using Carbon Copy Cloner (which is excellent software btw - I could have used Time Machine but I feel CCC is more flexible and works for what I need. All these HDs are less than 50% full as well.
With this new setup I can call up orchestral arrangements I had done before that had a variety of frozen tracks and Bounce-in-place stuff and they just play effortlessly with everything unfrozen. Same with any old arrangements that were bordering on CPU collapse of pop-rock stuff. Working on new tunes is way faster and easier as stuff just runs without CPU overages, and the disk streaming for samples is very quick.
Now using Logic X and Pro Tools 11 is a treat, as they are really both rocking with the extra power. Logic X 10.1 is especially sweet with a lot of new features.
If I compare the other main contender when I bought this 5,1 was to buy a new mac pro 6 core I figure I saved a bit of $$$ as I used all my existing HDs and SSDs and my UAD quad card. Had I moved to a new Mac Pro 6,1 I would have had to buy a new UAD system (as for some crazy reason they changed the way thunderbolt peripherals are addressed on the 6,1 and you can't put a UAD quad card in a TB chassis and have it work) and I would have had to re-configure my whole HD scheme - which would have cost me at least an extra $1,000.
The only things that concern me at this point:
How long Apple will support the 5,1 mac pro with their OS. Its qualified for Yosemite - but how much beyond that who knows.
Lack of Thunderbolt ports - not necessarily because I need the stuff, but just that a lot of interfaces and peripherals are moving to TB connections.
