Building on the earlier suggestion, I have been pretty disappointed with how some of these newer cards handle high-bitrate 4K files without stuttering. Before we get too deep into the parts list, could you clarify which editing software you plan on using? Whether you are on Premiere Pro or DaVinci Resolve makes a massive difference for which GPU architecture actually works.

• NVIDIA GeForce RTX 4070 Ti Super 16GB GDDR6X: This is probably the safest route for stability and the 16GB VRAM is great for 4K timelines, but unfortunately the price is a bit higher than it should be. Not as good as I expected for a mid-range build.
• AMD Radeon RX 7900 XT 20GB GDDR6: You get way more memory here for the money, but I have had issues with driver stability during exports. It just isnt as reliable as NVIDIA for professional work in my experience. Honestly, losing a project to a crash is way worse than overpaying slightly for a card that actually works...

Jumping in here with some technical data since I spent way too much time testing render times last year. When I moved from 1080p to heavy 4K files, I realized that raw clock speed isnt the only thing that matters. Its mostly about how the card handles hardware decoding and the bus width for moving frames. If you are building the whole rig for $1500, you have to be careful with how you split the cash. In my experience, you should prioritize:

• Hardware Encoders: NVIDIA has the edge with NVENC, especially if you move to DaVinci Resolve. The NVIDIA GeForce RTX 4070 12GB GDDR6X is basically the sweet spot for your budget. It stays relatively cool and handles 4K timelines without needing proxies most of the time.
• Memory Bandwidth: 4K textures need room to breathe. The 12GB on the 4070 is decent, but if you can find a deal on the AMD Radeon RX 7900 GRE 16GB GDDR6, that 16GB of VRAM is much better for heavy color grading and noise reduction.
• The CPU Factor: Since youre building from scratch, dont ignore the CPU. I found that using an Intel Core i5-13600K 14-Core Processor alongside an NVIDIA card is a great combo because of QuickSync. It offloads the decoding so your GPU can focus purely on the color grading and effects. I personally struggled with stuttering until I swapped to a high-speed NVMe like the Samsung 990 Pro 2TB PCIe 4.0 NVMe SSD. Even the best GPU wont save you if your drive is too slow to feed the data... basically the card just sits there waiting for the files.

You might want to consider the NVIDIA GeForce RTX 4070 Super 12GB GDDR6X since it fits your budget well. I would suggest being really careful with VRAM though... 4K eats it for breakfast. I learned the hard way that 8GB just wont cut it for smooth playback, so you definitely need at least 12GB if you dont want your preview window stuttering like crazy.