If you want the 27" screen size the only area you could really get away with downgrading would be:
- Processor choice
- Graphics memory
Given the work load you indicate you could easily do fine with the i5 and 1 GB card. If you do large amounts of gaming then maybe the 2 GB graphics card. Upping the RAM to 8 GB would be where I would put my money.
If you do video editing / audio editing / statistics applications then the i7 processor and 2 GB graphics card (video editing benefits on this one) would be a very good idea.
That said, if you have the money to spend, why not get the fastest machine? Just up the RAM at some point. 4 GB is good but programs get more and more memory hungry as time goes on.
My 3 and a half year iMac Intel Core 2 Duo 2 GHz 3GB of RAM see the link below for a complete tech specs
is more than enough for my typical usage.
I don't play games and I don't do programming
I use the computer mainly for internet.
Managing my work stuff, my music library, watching movies and I play a lot in Terminal.
So do your math