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Get 4 if you can wait a bit longer for BTO (it's still pretty quick). I don't mind 1.4GHz CPU, but 4GB of RAM is really a MUST.
 
You can get by on 2GBs...but you'll find yourself running out of ram pretty quick - which get's frustrating.

If you want to run more than four or five apps at once, or if you want to run two powerful apps at once you'll be wanting 4GBs.

On my old 13" MBP with 2GBs, whenever I'd try to run VMWare + anything else my machine came to a standstill - lack of processing power wasn't the issue, it was lack of ram.
 
Depends on your needs and what/how many apps you use simultaneously

Personally I would fork out the extra $$ for the 4Gb to future proof it

There, I made a reasonably well versed couple of sentences. I was going to say..

"hello! -- is there a brain in there?" and what not, but thought I'd consider your unique situation as a user, I must be getting tame in my old age
 
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