For a given bitrate, what video resolution is perceived as the highest quality? I'd like to achieve certain approximate bitrate for video encoding. If I use higher resolution like 720p, I'll get more fine-grained image, but more encoding artifacts. If I use smaller resolution like 480p, I'll get less detail and more coarse image, but higher image quality. Naturally, if the resolution is too high or too low, the result will be bad. Is there any research or information based on experience, what's the optimum resolution, given a desired bitrate and codec (in my case libx264)?
In case of H.264 codec, you can use YouTube recommendations.

Here's Vimeo video compression guidelines