personally I have the 2.4GHz model, and it runs beautifully, I can do everything from hardcore engineering work, or watching 1080p movies...the extra 100Mhz isn't really going to make a BIG difference in MOST tasks, granted these is double the cache, but still...
The 320GB hard drive is about $70 for a good quality one on newegg...BUT seriously, I have tons of 720p and 1080p movies, and the between the 250GB internal and a cheap external, I have more than enough room...
The 4GB RAM on newegg is $80ish, but it will get cheaper...and a year or so from now once the 4GB modules are cheap, you can easily get 5-6GB for the same price. In all honesty, I have run virtual machines (Win. XP), and still never really needed any more RAM than the standard 2GB!
Last, the added graphics memory, well, maybe a few frames in Crysis, but nothing really noticeable...
Trust me, I have done everything from basic office to engineering software like MATLAB, to gaming like Call of Duty 4/5 and Crysis...and I have never really felt a need for anything more.
Save the $520, and later on, you can upgrade to 500GB and 6GB of RAM for a FRACTION of $520!
Good Luck.