It sounds like you've already made up your mind.
I'd suggest to you, that you count "consistent" computing loads,
as part of the budget process. If there is a computing task you
only do 10-20 hours per year, then buying "extra iron" for that.
might not make a lot of sense.
To give an example, say you download a lot of movies, then change
the format for usage on media servers in the house, or to run
on your iPod or something. Movie rendering can use more than
one core (depending on the program you're using). If you generally
are always rendering one movie in the background, while doing
other work, then that would count as one or more "loads".
In your example programs above, Office may "run on 8 cores",
but not in terms of its actual usage pattern. I understand,
a recent innovation in Office, is for Excel to be multi-threaded
on basic spread sheet calculations. Now, some people do
financial calculations (for speculating on the stock market),
that run for hours. If Excel only forked two threads while
doing that, perhaps you'd count that as "two loads".
Your multi-core processor, is a "basket" of computing power.
If you're a multi-tasking person, with movie render and
stock market speculator running flat out, while you're trying
to burn a DVD, then perhaps a quad is a good purchase. If
your needs are more modest, you'd find the quad is largely
Even programs which claim to be multi-threaded, aren't that
way in all usage patterns. For example, Adobe Photoshop has
half its filters single-threaded, and the other half are
multi-threaded. And a particular version of Photoshop from
a few years back, for the multi-threaded filters, was only
running them on two cores. You need to understand the
limitations of each program, to decide how many "loads"
the program counts as.
Microsoft Flight Sim FSX, is an example of a multithreaded
game. But it has a limitation, as to how many useful threads
it launches on the fly. The program task can only be
split into so many pieces (map lookahead, current frame
render, AI planning of interfering airplanes, or whatever).
Eventually, even a well written program like that,
runs out of useful things to do with the cores. So if
I bought a dual socket motherboard, and put Hyperthreaded
hex core processors in there, would FSX run faster ? No.
And it's because there is a limit as to how finely, any
computing task can be chopped up. Games are particularly
bad, because the "boss thread" tends to be the limiting
part of the design. (On a quad, core loading is 100-30-30-30 %).
In the case of Photoshop, the design intent at Adobe, is
to prefer "accuracy" over "speed". For example, when an
image is rotated 5 degrees clockwise, 72 times, the resulting
image should be back in the same orientation it was originally.
But the image could be degraded, by the 72 image transformation
operations. Adobe picks algorithms, which give as little
degradation as possible, in that kind of test case. In some cases,
it means the filter design, can only be run on one core.
And that's why Photoshop is "half-multithreaded". So when
some bozo in a computer shop, tries to sell a $5000 computer
to some naive photographer, most of those computing
resources will be wasted. And each new version of Photoshop
can change that (like the two thread limit, was fixed with a
And the computing industry, doesn't do a good job of
communicating how their programs use the cores. So you
can't even be a "smart shopper", go to the Adobe site,
and get info on how multiple cores would help you. You
have to learn of these things, by reading forum postings.
On computing tasks that "scale perfectly", you get a
roughly linear speedup, with cores and clock speed. But
there really aren't a lot of programs that fit that
description. In terms of benchmarks, only Cinebench comes
close, and if you look at how the program works, you'll
realize it's "cheating". (I recommend downloading
Cinebench, just to watch the GUI while it runs. Should
be fun on your i7.)
So when you buy that hex core processor, most of it is
going to be idle, most of the time. It's like owning
a 600HP car. The speed limit in the city is 30 MPH,
you can burn rubber for the first two seconds, and then
you're at the speed limit. The engine gets 5 miles to the
gallon. And makes great sound effects.
For 10-20 hours per year, I'd love to own a quad. But
for the rest of the time, the dual is fine.
I have one other data point to share. I was given a laptop
as a gift. It runs Windows 7. It has a single core processor
(the horror!). Yet, Windows 7 does a surprisingly good job,
of working with only one core. For example, I haven't
seen any "stutter" effects, like I've seen on previous
single core desktops, running older OSes.
In my testing so far, performance remains acceptable, until
I install a certain webcam software package. Even when the
webcam is unplugged, the laptop runs slower. I have a feeling,
if the laptop had a dual core, that side-effect of bloat,
would be less evident. And hence, why I recommend to people,
that a dual core be a minimum solution. The single core works,
and for example, I can web surf on that machine just fine. But
I can't leave the webcam software installed (Logitech should be
proud of themselves).
Even the designers of the processors, are aware of the usage
pattern issues. That is why they introduced "Turbo" (faster
clock speed, when only one core is being used).
The AMD hex core, has an option to turn down half the cores
when under light load. Internally, if you look at a silicon
die photo, it looks like two three-core processors living
on the same silicon die. And like one of those engine designs,
that turns off half the cylinders, the AMD design can save
some power, when it's not being run flat out. The configuration
can be changed relatively quickly (100s of microseconds). Actually,
you'd be surprised how many tricks are being used now. And
how transparent they are to the user.