Rendering at a higher resolution won't do shit, it'll just take longer to export. All you're doing by increasing the resolution is stretching out the image from the original size. It'll look worse on a 2560x1440 monitor when viewing the video at its native resolution (not fullscreen), because you'll be seeing a 2x stretched image instead of the original video quality.
YouTube wont look any better or worse, it will just take longer to upload, and give you the option to watch the video at the "original" resolution.