Modern video codecs work by dividing the video into macroblocks of 16 x 16 pixels. This means your encoder needs resolutions that are evenly divisible by 16 (or at least 8). Trying to make a video with a height of 1050 will produce a video with "garbage" information at the edges, since 1050 is not divisible by 16. This will degrade the quality of the encoding, or give you very inefficient compression.
You should encode to standard 720p or 1080p (depending if your source is HD to begin with) and let your player or tv screen scale the video.
Edit: And Olyteddy is right about not converting standard def to higher resolutions. It will simply degrade the picture quality.