1. All motherboards work with all PCIe GPU’s. PCIe is a platform agnostic standard. If your motherboard is old enough that it does not support PCIe 4.0 though, you should definitely upgrade, because that probably puts your CPU as being old enough to bottleneck a 4070.

2. Again, platform agnostic. there are some internal benefits for running all-AMD hardware, but they’re minimal. Intel will work perfectly well. Refer to point 1 to see if you should upgrade or not.

3. Generally they mirror Nvidia’s numbering scheme. Aka, the x900 GPU’s are the halo card, followed by x800, x700, x600.

Unfortunately AMD’s current lineup is a little behind in the midrange market. Their only midrange cards in the current lineup are last-generation RDNA2 6000 series cards aside the 4060-targeted RX 7600xt, which puts the closest AMD equivalent to the 4070 to be the RX 6900xt/6950xt. The 6950xt is currently floating around that 600-700$ pricepoint that the 4070 is at, and roughly matches it in raster performance.

Raytracing is significantly worse though, it uses more power, and AMD’s software stack (frame interpolation, recording/encode, etc), while usable, just isn’t quite up to the same par as Nvidia’s. So if any of that really matters to you, I unfortunately have to recommend the 4070.
However, if you can handle those downsides and just need to play traditional raster games, please please buy the AMD card and do not feed Nvidia’s idiotic greedy monopoly machine. Jensen is smoking crack and the last thing anyone needs to do is feed that man’s overinflated head more fucking cash.

Or even better- wait until 2024 if you are not in need of an immediate upgrade. Intel’s first generation Arc GPU’s had a rough launch but have improved massively over the past year with driver upgrades, to the point of being fantastic first generation products. Their second generation Battlemage GPU’s are expected at the beginning of 2H 2024 and could potentially be a killer value in the midrange segment.

Do I need to buy an AMD CPU as well? Or can I use my existing Intel CPU with an AMD GPU?

You don’t need an AMD CPU. Smart Access Memory (aka Resizeable BAR), which is what you’d be seeing if you try to research matching AMD CPUs and GPUs work with any combination of CPU and GPU. Yes, even nVidia GPUs have ReBAR now. SAM is just AMD’s marketing term for ReBAR.

AMD is currently lagging behind in the temporal upscaling department. This would be your DLSS, XeSS, FSR, and game engine-specific temporal upscalers. DLSS3 is currently the best of the lot but is locked to nVidia cards because of the way it works. It requires the Tensor cores only found on nVidia GPUs. The main reason to use these upscalers at the moment is to get usable FPS when running Ray Tracing at high resolutions. It can also extend the life of your GPU by allowing it to render at lower resolutions and upscale to higher resolutions. Ie 1080p -> 1440p. Fair warning that nVidia’s DLSS implementations aren’t very backwards compatible since they rely heavily on GPU architecture. FSR and XeSS are theoretically platform agnostic but XeSS is better optimised to be run on Intel’s ARC.

• For 1, all motherboards should work with both AMD and Nvidia GPU.
• For 2, you can mix and match, there are some benefits to using both an AMD CPU and GPU, namely Smart Access Memory
• For 3, AMD’s naming is confusing as hell but basically they used to have R3, R5, R9, etc for different tiers of cards, but now everything goes under the “RX” naming prefix.
• They use the X and XT suffix to differentiate the fastest versions of the same tiers of cards or revisions of cards. (Kind of like Nvidia’s TI suffix)
• The equivalent of a 4070 is a RX 6950 XT as far as I’m aware.