Good game, it's definitely nice to win against someone 700 points higher than yourself. I noticed Rxc8 while flipping through but I guess being down to a few minutes of time can rush you a little.
However I dont think sacrificing a knight in the middlegame is enough to call it an immortal game ;)
So I played a not so awesome game against a guy rated 700 point above me and won, I am getting it analyzed, but I think I played extremely well if not perfectly (edit, I found a line where white is winning, but it is (less than) far from obvious). Check out the game and tell me what you think.