When it comes to bitrate, you really need to start with the normal Internet connection speed of your viewers and then from there, you can determine what the optimum dimensions will be.
If you start with fixed dimensions.. then if you need a higher bitrate to produce the best quality, you may well exceed the download connection speed of your viewers. If that happens, you have to decide if your viewers would rather suffer through multiple start/stop as the video buffers or if a little less quality would be better.
That being said, let's create sort of an approximate formula for bitrate per dimension.
To start, lets say that a 320 x 240 video will display a good quality video at a bitrate of 350kbps.
So 320 times 240 = 76,800 px
1000 x 517 = 517,000 px or 517,000/76,800 times the area = 6.7 times the display area.
So to "paint" that area would require about 6.7 times the amount of "paint". In our case, it's "data", not paint. But it would still require approximately 6.7 times the amount of data that the smaller video would, to produce the same quality.
So 350kbps x 6.7 = 2.345Mbps. So for your video with dimensions of 1000 x 517 to have the same quality as the 320 x 240 video, you would need a bitrate of 2.345Mbps.
This is a VERY HIGH bitrate and most viewers would have problems downloading videos with bitrates higher than 1000kbps.
Keep in mind that this formula is just an approximation... but the math is real.
So starting with set dimensions is a problem because you can't do anything to increase your viewers Internet connection speed.
To improve quality at any given bitrate, reduce the display size.
Best wishes,
Video Man