The SSD kept it going for a bunch of years, that is the key upgrade on an old machine. The RAM helped of course, and the Video Card makes a difference, especially with Lightroom 6 now being GPU optimized. However, the upgrade to the 3.2 Ghz processors was a definite mixed blessing. The 15% speed improvement is actually noticeable, but the TDP on the processors went from 80 watts to 150 watts, meaning an additional 140 watt draw when they were going full bore. It was enough that I could tell when a Lightroom slider was not one of the ones that used the GPU, because if I started tweaking one, the fans would start to roar. Pretty ridiculous.
So I thought about getting a newer machine, but the latest Mac Pro came out two years ago, and doesn't have room for the hard drives in the 2008, or the Video Card I got for it. Arguably the machines, expensive as they are, are a good deal. If you look at the going rate for the video cards in the NMP, especially the high end ones, it looks like you are getting over $1000 off by buying them in the NMP, and they throw in the rest of the computer for free.
However, it was not clear to me that I really needed $6000 worth of Video Card, even at the $4000 bargain price. Also, they came out two years ago, and the best deal you can get from Apple is 15% off on a refurbished model. That didn't sit well with me.
I spent a while trying to figure out if there would be a new new Mac Pro (nNMP?) any time soon, but Apple is notoriously tight lipped. The scuttlebutt seems to be based on when the correct Broadwell Xeon parts will be available, which should be later this year, since Apple is likely to skip Haswell altogether. Unfortunately, the usual tick-tock Intel schedule was badly disrupted when they shifted to 14nm, and Broadwell is really late. In fact, Broadwell was followed very quickly by the 'tock', Skylake, which also comes with a new chipset, the 170. The 170 has a number of cool features, including support for DDR4 RAM.
At any rate, I decided to build the following machine:
ASUS ROG Maximus VIII Hero Motherboard
Intel i5-6600 CPU
Cooler Master Hyper 212 EVO
EVGA 750W Gold PSU
G.SKILL Ripsaws V 16GB RAM
Samsung SM951 SSD (512Gb)
Syba Firewire card
realtek chipset Ethernet card
Fractal Design R5 Case
I already had:
2x Sandisk Extreme Pro 960 GB SSD (for Lightroom library)
EVGA Geforce 750ti
LG Bluray/DVD burner
I got the i5-6600 Skylake instead of the i7-6700k because at the time I built it, the overclockable 6700k was selling at about $440, instead of the MSRP of $350. The 6600 was available at list, and since it has a TDP of only 65W, as compared to the 95W of the 6700, it seemed the better choice for a "cool" and "quiet" build. Overclocking is definitely not compatible with cool or quiet. However, even with the lesser processor, performance is more than adequate, the system benchmarks better than a 4 core Mac Pro 2013 (the low end of the new round ones).
The Fractal case, and the Hyper 212 EVO were also specced for quiet. Both are very well reviewed, and my experience matches that. I did have a problem with case, but Fractal design sent me a replacement side panel that fits perfectly. The 6600 comes with an Intel cooler, but some of the reviews complained it was noisy, so it was replaced by the 212 EVO. The Z170 motherboard is arguably overkill, but it supports the high speed RAM, and should be reliable, as it is overbuilt. The PSU is also overkill, but it seems cheap insurance for longer system life, and since it doesn't run the builtin fan until it reaches 45C (which it never has) it is another contributor to quiet operation. You do have to be sure to set it for ECO mode, or it will run the fan all the time.
It also seemed a good idea to get a modular PSU, this was my first build, and modular PSUs are supposed to be easier. This one certainly was not a problem, even with the several disks (not listed) that I also put in. If I do get a higher powered GPU (when Pascal arrives later this year?) I will easily be a able to power it as well.
Putting it together was pretty easy. Getting it to boot up as a Mac was a bit harder, but the good people at tonymacx86.com helped a lot. They still are not recommending Skylake builds, only Haswell or Broadwell, but it really was not that bad. It took me a while to get iMessage working, I had to follow this recipe from Reddit. Until I did, it kept telling me that such-and-such number was not registered with iMessage, when I knew perfectly well that they were. I still have problems with sleep, but since some of the software I use doesn't like sleep (looking at you Kyma!), that is not such a problem.
P.S. If you have read all this, you might wonder why I put it up. I was encouraged to do so by a scientist friend at LANL, I guess computer builds have to be interesting to somebody, right? He, by the way, is very happy with his NMP. The only thing I envy him is that the case on this thing is really big ...