Will upgrading to 16GB of RAM boost my 4K gaming frame rates?

Not really. At 4K, your GPU is the bottleneck almost every time, so adding RAM doesn’t make frames go up. 8GB is still enough for most games at 4K; the extra 8GB helps avoid stutters if you run many background apps or memory-heavy games like Cities: Skylines with mods, but it won’t raise your average FPS. If you already have 8GB and get low frame rates at 4K, your GPU is the problem—spend the money on a better graphics card instead.