Interesting. MBP (8,2), with 16Gb is sitting here doing not much (1 x Preview window, Cal, Mail, Contacts, Notes, 9 x safari tabs, Messages and a single Excel sheet) and I'm using 6.3Gb.

I also have 23 million page faults in a VM that I didn't know I had!

Is the i7 much of an improvement over the i5 then?

Dual Core i7 are 15 to 30 Percent faster generally ( [Depends on which i5 and i7 even within same generation] Quad Core in 15 inch) is around 2X Faster.

Yes Apple with Airs and Retina ushered in Ultrabooks (the copies). These tend to have Soldered Ram to save space on sockets and allow for denser packaging in general.

Of course having options is nice there just BTO now. Apple while charging a bit of a Premium as do all manufactures is not totally out of line. It was nice to be able to do it later when prices came down or a process shrink allowed for denser modules aka when we could go from 4 to 8 or 8 to 16 in recent times. That said systems could not aways handle the new modules, not addressing all of it etc.

Moot point now its soldered in all but some Mini and iMac.

Here is Geekbench... Be sure to Click on 64bit Muli Core Tab

http://browser.primatelabs.com/mac-benchmarks

There are also test in bare feats.com and macworld, etc.

Remember that not all programs are Multicore aware and some top out at how many cores can be used. That said. Having at least a Quad Core is usually very helpful as Applications and OS have more to work with and most can and do take advantage of it.

Note too that Apple and others tend to bundle sometimes a good thing More Ram, More SSD Size, Better CPU/GPU in the higher end i7 configurations.

Sometimes it really is a free lunch adding 1 or 2 of these tops the price of the higher end model which may include it. If the options really do not make sense there not even offered, you will find them bundled in the higher end configuration.

And while I use to think Apple's choice were a smudge less flexible try looking at Dells for example there Gosh Awful. They for example just speaking of RAM, SSD and CPU not going in the terror of Monitor resolution choices on Win7 vs Win 8 machines..

You will find that there XPS15 selling for around $1700 to $2200 but offering almost no configuration options. Zero Ram options, no SSD except a Combo of an HD and small semi useless mSata 32gb. In order to get something similar to a Retina 15 you have to jump to a M3800 precision workstation starting for around $2500 and it does have good configuration options but again their tiered into Preset packages which then can be modded some.