GPU/MoBo Combo with Ryzen 9 3900X?

Greetings Rujellis. Board selection can be pretty tricky as it will depend on which features you will need as well as your personal preference for aesthetics. When going with a Ryzen 9, I'd highly recommend the X570 chipset as they tend to have better VRM cooling to allow the processor to maintain it's boost clocks without issue. The X570 chipset also offers the widest range of chipset features as well as PCIe 4.0 support, something that will become widely adopted in the next year or so.

Does your $1000 budget only pertain to the GPU, motherboard and CPU? If so, the Ryzen 9 3900X currently is listed at $479.99, which leaves $520 to be split between the GPU and motherboard. For 1440p, the best price:performance is likely going to be the Radeon RX 5700 XT, which starts around $360 for the dual fan cards: https://www.microcenter.com/product/611002/powercolor-radeon-rx-5700-xt-dual-fan-8gb-gddr6-pcie-video-card. This leaves a total of $160 left for the motherboard selection ($180 if we count the $20 discount bundle). Here is a list of our boards from the $100-$200 price range: https://www.microcenter.com/search/search_results.aspx?Ntk=all&sortby=match&N=4294966996+4294818892+4294810816+39&myStore=false. You will need to determine which board looks best for your preferences, and which board has the features you require for your system. If you wanted to compromise on graphics performance, you can find the regular RX 5700's for $300, which is 20% cheaper and only performs around 10% slower on average: https://www.microcenter.com/product/608896/powercolor-radeon-rx-5700-single-fan-8gb-gddr6-pcie-video-card. That would allow you to move your motherboard budget up to around $240. Ultimately, the budget for your board will depend entirely on where you can compromise for the GPU. For 1440p, it really depends on which graphics settings you plan to use and which refresh rate you are aiming to hit. If you have any further questions, do let me know.