Well, my thoughts are, RAM will be easily replaced or added to, etc....and likely can be had for a good bit of discount 3rd party than by Apple BTO (Build To Order).
While you can swap out your CPU.....I'm going to go with the best I can afford at BTO, but will add more RAM almost immediately after I get the computer, likely from
Crucial ....like I've done in the past with my MBP.
You can get more bang for buck doing RAM additions / replacement after purchase than you likely can with trying to later upgrade your CPU. CPUs cost a bunch more than RAM and what do you do with our old CPU you're replacing?
And I figure 1TB for a system HD is plenty (the SSD). I mean, I don't store that much on it that is NOT system required stuff. Applications and system stuff.
But right now, I have a couple (soon to be more) external thunderbolt drives. I have one that is a SSD external that is dedicated as cache only to the applications that need it.
My other external drive, is where I keep my media....pics, video, etc.. So while I'm editing, I cut down disk I/O...the system and applications work on the internal HD, the media is worked on its own drive and cache values have their own drive.
At least that's how I see it.
HTH,
cayenne