im also struggling to get the price down and i think i could do with a better case ...
looking for a kinda white and rgb theme ha ha
If you want to save money, dump the AIO - and get the Dark Rock 4 or Dark Rock Pro 4 - that will save you £80 to £60 and will also look stylish in a windowless case. Also, less points of failure and on a par for cooling. There are cheaper, great coolers but the Dark Rocks may sway you with their looks.
That's a budget x570 - for gaming, I would get the B550 (MSI Tomahawk or Gigabyte Elite) - superior VRMs and no fan. Still retains PCIe 4.0 - only on the GPU and first M.2. slot - but more than enough for gaming. Plus, when you upgrade the Gen3 NVMe would pass onto the next M.2 slot if upgraded to a Gen 4.0 (but zero real life gains for gaming). Plus, MSI are doing cashback offers - for motherboard bought with a Ryzen CPU - so more savings to be had (but most manufacturers have some promotions going on - Gigabyte are giving away 500GB NVMes).
You can get a 10 year warranty PSU for the same price - Corsair RM 750W or Phantek 750W. The SuperFlower, although a decent unit, only has 7 years.
Do you need all that storage? If not, I would be tempted to get a 2TB NVMe - a 2Tb ADATA SX8200 can be had for ~£200 5 year warranty.
Memory - with the time between your system builds I would consider 32GB - the 32GB Crucial Ballistsix 3600MHz are only £140 and have tight timings.
And yes, the 5800X would be faster in games than the 3900X - due to the showcased 19% uplift. But at 4K the GPU will be taking a lot of the strain - a 3700X can be had for ~£260 or even a 3600 for ~£160. You could always update the CPU in a few years time...