CPU: AMD Phenom II x4 BE 3.2 Ghz executed at 3.6 Gz (OC type Phenom II 955)
While this was a great Processor, it simply isn't powerful enough for your Graphics Hardware or Operating System.
I mean you can "Get Away" with using it... but you're going to have a bad time, just like if you were to use it's competitor the Core 2 Quad.
Sure, on the Task Manager it might not look like your Processor is being utilised much... what this comes down to is that Processors from 2008 - 2010 aren't really designed for the Modern Asynchronous Tasking Environment that Windows 10 has.
It's actually why despite Ryzen 1st and 2nd Gen being "Lower" Performance in Raw Core-to-Core Performance., in terms of Desktop and Multi-Core Performance they make Intel look like a joke.
And that's due to the Asynchronous Architecture that started with the Phenom II., the key difference being is that something like the R5 1600 has 3x Asynchronous Threads and 2x IPC (Clock-for-Clock) ... which is kind of apt here as it does (Stock) run at the same Clock Frequency.
But you also have other aspects here to consider... such-as PCIe 3.0 Support (which I'd wager your Phenom AM3 Board doesn't support) and Compute Performance wise that's important as Compute uses more Bandwidth, which you're essentially halving.
As well as Memory Frequency., which again DDR3 has fewer Concurrent Lanes over DDR4... so it isn't just a case of a Frequency but Latency difference to consider that does determine the Bandwidth Available.
Now the last thing to point out is that unless the Application you're using is SPECIFICALLY using OpenCL (Compute)., then using "Compute Mode" instead of "Gaming Mode", is only going to result in Lower Graphics Processing Performance for Non-Compute Pipelines. (Typically by ~10%)
The last point I'll make is Prepa3D 4.5 (according to the Release Notes) actually removed support for HLA (High-Level Architecture Acceleration)., likely to make the program more stable on Modern Hardware; but this does mean older Architecture (like Phenom II) is going to see a noticeable drop in performance (and utilisation).
I can't see any information (at least at a glance) that it requires / uses Compute (OpenCL or CUDA) ... but I did notice that they seem quite proud of their support for 64bit Architecture., which likely means it's Optimised for Workstation Processors and Graphics.
You might find that you'll be better off with a "Cheap" Threadripper (like the TR-1920X., which is ~£200 now)., while you're GPU you'll want to Custom Flash (switch the BIOS to the Secondary Position) to a WX7100.
Note: You can't just do this directly, but if you look about; you should find some "Modified" Versions of the BIOS that'll let you do it.
Trust me, the Radeon Pro Drivers are typically better for things like this ... it's just I doubt you have a spare £570 for what is essentially the Radeon Pro RX 480. Been a long time since the Workstation and Retail Cards have actually had more than cosmetic differences.
