I had an iMac 5K, it was great! It had a problem with strange colors and artifacts on shutdown. On day 14, I decided to return it rather than have a brand new computer repaired. I have since found out it is likely a software issue with Sierra and probably not a hardware issue. So now I am debating if I want to just buy the same machine again, or go with something totally different. The machine I bought, and would buy again was a 27in, 4.0ghz i7, R9 M35 2GB with 1TB flash. My most demanding needs are for business, and they include: processing RAW photos with Lightroom and editing with Photoshop, technical design with Illustrator and Microsoft Office Suite products for word processing and Excel spreadsheets. Beyond that, I also run a few applications on a Parallels Windows VM. The iMac seemed to be able to handle all of this with ease. I do not play games or do anything with video editing. The problem is, I am starting to dislike how disposable Macs have become. That 5K iMac is so difficult to open and future expandability is pretty much none other than peripherals. I have had Macs since the llc and Macintosh days, and this is the first time that I have started to shop around for a Windows machine instead of buying the next model Mac. In the past, I was always tied to Macs because I had a lot invested into Adobe Creative Suite. Now, I am still running CS3, so beyond ready to upgrade to CC. Switching to Windows wouldn't be a big problem financially. But I am really comfortable on Mac OS, changing would be a difficult learning curve. This brought me to start looking at the older Mac Pros. I have spent a couple days reading up on the 5,1, and it seems like it can be configured to outperform the 5K imac for less money than the 5K(without a 5K display, but that's acceptable). I was looking at a 6, 8 or even 12 core 3.46 Westmere. Geekbench scores are higher than the iMac 5k on the 12 core machine, but single core scores are around half that of the 5K. This is where I am wondering if the 5,1 is a good choice or not. I know my way around Macs, but I am really confused by things like performance of processors and graphic cards. I know that some applications use multiple cores and some don't. Also, I know that while my older version of Adobe CS relies a lot on processor, the new CC I think utilizes the GPU better. So I would look to get a decent GPU if I go with a cMP. I have found some evidence that suggests anything beyond 6 cores doesn't provide much performance boost with Photoshop, but that might have been with older versions. I know that Microsoft Office Suite does not have multi-core support at all, and I don't know how much performance will take a hit on that. I use some pretty large spreadsheets with lot of formulas. One other thing I was not able to find out is, if you have two identically clocked processors, do a 4 core and 6 core perform equally on a single core? Or do you take a hit on single core performance when you add or subtract cores? I'd like to know if anyone has any thoughts that will help me decide which way to go on this decision. I just don't want to be disappointed by purchasing an older cMP and finding it doesn't perform well enough. There is nowhere to go test it out, I just have to buy it and try it out. That feels too risky for me because I need it to work for my business. I am also well aware that I can spend far more money on the cMP getting it to perform as well as the 5K. But a least I can do it in stages and I have the option to upgrade components instead of having to buy the iMac configured with more to accommodate for my future needs. Thanks for taking time to read my long post. Any advice is welcomed.