I play with this guy sometimes who has a pretty old standard definition TV, and he used to tell me I was a noob for using holographic sight because it was exactly the same as red dot except the dot was huge so less accurate, and I couldn't understand why he wouldn't believe me when I said it was much smaller, it just has a sort of ring thing around it like a target.
But yeah, whenever I play on SD or even on a TV smaller than my own (32 inch) I fail horribly, I just don't see people that I would normally kill with ease.