Help me choose: Dell with T4200 to T6400?

I am getting a Dell Inspiron 15 laptop for my wife. She mostly does Word, Outlook, Excel and web surfing. Some streaming online video. No games.

The base system has the Intel T4200Dual Core (2GHz/800Mhz FSB/1MB Cache), with 3GB shared dual channel DDR2 at 800 MHz and Intel Graphics Media Accelerator X4500HD for $450. Vista.

If I upgrade to a nIntel T6400 Core 2 Duo (2 GHz/800Mhz FSB/2MB cache) it is $35 more.
If I upgrade to 4GB is is another $25 more.
If I upgrade the Dell Wireless 1397 802.11g to the Intel WiFi Link 5100 802.11 Wireless-n it's another $35

Recommendations?
1) Will there be a noticeable increase in speed with the 6400 over the 4200? (What is the difference if they're both 2GHz and 800 Mhz?)
2) Is the old rule of thumb that you can never have too much RAM applicable for this situation, or is 3 sufficient?
3) Is 802.11n worth it?

Are these upgrades worth $100 more on a $450 machine?

Thanks!

Thanks frozenlead. I thought "n" was becoming the new standard, though not currently in use.

+1 ^
Memory - Unless you go with 64 bit operating system, ONLY about 1/2 gig of that 4th gig will be usable. ie w/3 gig you have about 3 gigs available for OP and programs. W/4 gig ram you will have approx 3.5 gig available (or less) for op system and programs. This is due to memory mapping with a 32 bit operating system.

Processor, I would go with the T6400. The T6400 is a newer proc and more efficient Processor. Although again I dought you will notice any performance diff on most tasks. But there may be a small improvement for newer programs and there may be a small advantage in terms of power consumption and, or Heat disipation - for Only $25 I'd go with the newer Proc.