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If my 3,1 dies, I'll buy an HP workstation or something. WIN-DOS, not hackintosh. Therefore also no need to invest in a new Iphone.

OS X was a killer OS for a while, but it is losing ground, and is becoming as bug ridden and bloated as WIN-DOS was before.
Why do you say "WIN-DOS"???

There's no DOS in Windows (at least in this millennium).
 
I recently bought a power supply for my 4,1 just in case the worst were to happen (it was a bargain too), if it completely failed I would only get another 4,1/5,1 if I could get it for as good a price as this one, if not I would probably build an X79/X99 based system from used parts.

From eBay?
 
I recently bought a power supply for my 4,1 just in case the worst were to happen (it was a bargain too), if it completely failed I would only get another 4,1/5,1 if I could get it for as good a price as this one, if not I would probably build an X79/X99 based system from used parts.
The power supply in my 2008 Mac Pro 3,1 died a few years ago I found obtaining a replacement power supply a struggle. Ideally I would have bought a new one but these were unavailable. I eventually paid £150 for what was described as a used one but when it arrived it was clearly brand new. Nowadays it would be nearly as cheap to buy a whole working 3,1 system.
 
Performance wise how would a new iMac compare as I see a second-hand 2017 model are around 1500 quid or so..
 
Performance wise how would a new iMac compare as I see a second-hand 2017 model are around 1500 quid or so..

Unless you do 3d rendering or video encoding all day long (utilizing 8+ cores), any recent iMac with a dedicated GPU will be just as fast – or faster. Just make sure it has an SSD and enough RAM.

The iMac Pro outclasses all previous Mac Pro in regards to performance.
 
just compare cpu models gpu models and other parts to see potential speed change then add in the apps you need/want to use and if they can actually use the full potential speed of a part

ie if app x will only use 1-core of a cpu then 4c v 8c cpu will be mute it will just come down to single core speed, if there close in clocks the speed will be close.
if app x will use only 4-cores of a cpu then 4c v 8c cpu will be mute it will just come down to single core speed, if there close in clocks the speed will be close.

etc
 
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