For the things you are doing, the $450 one is probably fine.
With windows 7/8, unless you're doing something that requires a lot of memory, 4gb is fine (heck, I just upgraded the desktop system my son uses from XP to Windows 8 and that only has 3gb. works fine for the games he plays).
Seriously, browsing the web, watching youtube videos and whatnot, word and excel, even powerpoint dont require a beast of a system. I think a lot of people spend a lot more than they need to on computers.
If you had said you were editing a ton of photos with photoshop/lightroom, editing video, etc I'd worry more about processor speed, amount of RAM and storage. (and even then, my wife has a quad core with 6gb of ram and 500gb hard drive and it works perfect for editing RAW photos...and it cost under $900 2 years ago to boot).