I am currently debating which one to buy out of 2 mentioned above. The main differences are:
N551: 850m 4GB, 1000 SSHD (1000 HDD + 24GB SSD), i7 4710hq, 12GB RAM
N550: 850m 2GB, 1000 HDD, i7 4700hq, 8GB RAM
The main difference is that n551 is 90 $ more, and since I am already spending ~ 1200 $...