Advanced worldgen can make DF exceed 2GB trivially.
More than a few hundred MB during normal gameplay is unusual for most embarks.
The sad reality is there are remarkably few games that are multi-threaded, compared with the thousands of games stretching back to the 70's that are single-threaded. It is going to take many years before multi-threaded is standard, expected, and bug-free. I can replicate thread mutex-lock crashes on at least two of my computers, and this is since 2010. Multi-threaded applications are NOT stable and mature technology, when compared with the stability of single threaded applications. In fact, the only genre of computer games I know of that are under any pressure to be multi-threaded are MMO's, due to most people trying to run the game without sufficient 3D acceleration, and MMO developers making bonehead moves like offloading rendering tasks to the CPU instead of the GPU.
<rant> Seriously. Rift was artificially CPU bound and limited to 30fps. Why? The developers didn't want to "force" players to have a "top end" 3D accelerator to play the game. Great. Good job. Way to step back over 10 years in innovation with that one single stupid decision! And people wonder why I gave up on MMO's? </rant>
I've tried to explain this to my relatives who buy i7's, complain about heat/noise/power consumption, and then use the computer for exactly one task (surfing).
If you plan on running 8 VM's, sure, buy an i7. Otherwise, buy the cheapest possible processor you can find, and it'll still be faster than anything the average user could possibly need 99.9% of the time. Anything more is just a waste of heat/power, imho.