I would highly recommend you to go with a Ryzen 3 3000 series CPU!
For folding, you'll probably be ok with a quad core.
But it's really PCIE 4.0 you will want!
Those Ryzens run very efficient.
Motherboards from Asrock run great. It might run on 450 motherboards, but preferably use 550 or 570 (or 590) motherboards, as they natively support the Ryzen 3000 series CPUs (you don't need to buy a low end CPU just to do a bios update).
RAM prices are going up (due to COVID), but you should still be able to find some popular DDR4 3600 modules for $75 (for a 2x8GB set).
3600Mhz is a no-brainer, as they cost nearly the same as 3200Mhz memory.
For Intel, memory speed doesn't matter much,
But for AMD, memory speed is tied to it's 'infinity fabric', meaning the ring bus that connects all the CPU cores together.
Faster RAM means a faster infinity fabric, which means higher performance, even if the CPU frequency is fixed.
I've had some issues with Asus TUF motherboards, so I won't recommend them.
PCIE lanes is a lottery.
As long as you disable most of the unused stuff (SATA/Thunderbolt/other ports), you could potentially run PCIE x8/x8/x4 on some boards.
This as some boards 'borrow' an extra 4 PCIE lanes from unused ports (like USB, Wifi, m.2 slots, and other...).
The F doesn't have a built in GPU, perhaps they borrow the extra 4 lanes from there. I don't know.
But every CPU has at least 24 PCIE lanes (perhaps more), with 4 addressing the IGP (which is non-existent on core i processors marked with an 'F' behind them), and another 4 addressing North/South bridge, USB hub, LAN, m.2, PCIe x1 slots, and Wifi, ... Only 4 of them you can 'borrow' occasionally. The other 4 are fixed (can't steal them).
Resulting in 20 available PCIE lanes. Not all motherboards can successfully take them; which is why this is a 'lottery' of kinds.
But if you want more of a guarantee, MSI's MPG series for Intel's 8th/9th gen CPUs can run an x8/x8/x4 configuration (worked with my i5 9400F and Core i3 9100F).
If you run Linux, this will be sufficient for 2x next gen (future) GPUs from AMD or Intel, and 1 RTX 2000 series GPU of 2080 or less.
But even if your board only accepts x8/x4/x1 solution, if the board and CPU support PCIE 4.0, an x1 slot might work for an RTX 2070 equivalent or less in Linux.
Or, if you're planning to invest in GPUs in the near future, get a quadcore with SMT, or 6C/12T 3000 series CPU, with a board with lots of PCIE 4.0 x1 slots.
Right now, the only GPU running 4.0 is AMD's 5700XT; which isn't that efficient, but should fold well from a PCIE 4.0 x1 slot.
Like always, PCIE 4.0 is backwards compatible with 3.0.
However, by the end of the year, AMD (as well as Nvidia), will come out with 5000 core GPUs.
Things might get very interesting!
Though those GPUs probably will need PCIE 4.0 x4 (or PCIE 3.0 x8) minimum.
You probably also don't want to run too many of these on one PSU (300watt/GPU; possibly for Nvidia the mid range GPUs will still see a ~200W TDP, but the high end would see 290-300W stock).
In a few days AMD and Nvidia are supposed to reveal their new line of GPUs. Starting with the Mid-range 3000 series GPUs (2070 S / 2080 S equivalents).
By beginning next year we're expecting a base model from both AMD and Nvidia, that will be the equivalent of a 2060 Super, but at reduced power output.
AMD might still be a generation behind on power efficiency; meaning their new GPUs probably will equal current RTX 2000 series GPUs in terms of efficiency, but will outperform them.
Performance wise, the new Nvidia GPUs are expected to follow:
3060 = ~2070 Super,
3070 = ~2080 Super,
3080 = ~2080 Ti, and
3080 Ti > RTX Titan (by a ~20% margin).
AMD's equivalent will be similar in performance.
post edited by ProDigit - 2020/05/14 16:58:36