My system is about 5 years old now, i5 3570K cpu on an asus motherboard which is no longer available. I've 16 GB of slow ram, and recently installed an SSD and a graphics card and so long as the bits stay together I think it runs my photoshop, captureOne pro 10 and affinity photo pretty well, with no reason to upgrade to newer components. I did get an improvement when I made sure that the bios was changed to AHCI and as I had cloned the os I had to realign the partitions. Could not be happier with the old beast.
As for Affinity photo I think it can only improve, and at the price is a very good program. I hope over time it will mature and we get some people developing panels etc for it to help us along the way, but even now NIk works on Affinity. A great thing about Affinity Photo is the already long list of tutorial videos that are available.
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Nicely edited Claire.