Most of you probably find this question stupid but I have never seen a 1080p monitor before and I live in a rural area and cannot compare them in stores. I am looking to upgrade my 1680x1050 monitor (what p is that = to btw or is that impossible to say?) And would going higher than 1080p make any difference for blu-rays or youtube?
P is progressive scan, really has nothing to do with the resolution but more with how the frames are displayed. You could call it 1050p if you wanted.
1680x1050 is a different ratio from 1920x1080, so yes you would see a difference depending on what your monitors native ratio is.
And no, using a higher resolution than the media source will most likely actually make the quality worse. My friend has experienced this with a 4K TV he bought.
If the source is 1080p, use 1080p.