| second of all, you haven't any clue about multithreading. zero.

Multi-threading is not the issue.

https://en.wikipedia.org/wiki/Multit...%28software%29

A single core CPU has multithreading via
time slices. The advantage of multi-core is
that a single, intensive operation can have
a dedicated core, without locking up the
machine and without needing to share time
slices.

The issue is whether PS can actually
use multiple cores in any significant way. For
that it needs to be running two or more processor
-intensive operations concurrently. Do you often
run a sharpening routine on a 40 MB image while
at the same time running another filter? If not
then the sharpening will run faster with less cores
because the core being used will have a higher
MHz speed.

No one needs to go by what I'm saying. In
Windows one can run Task Manager to see usage
in real time. There may be something similar on
Macs. So rather than carpet-bombing the thread
with empty, un-qualified pronouncements and
insults, why not do some experimenting for
yourself? You can then decide what's best for
you. Maybe you'll find that PS is somehow running
your sharpening routine on 2 cores, but that's *very*
unlikely. The routine is a single operation that needs
to go through the image bytes with a math operation.
There just aren't two things to do at once.

Much of the time there's very little CPU
usage on a typical machine. If I do something like
run a CPU-demanding script then I'll see 48-50%
usage by that process, because I'm using a 2-core
machine. Meanwhile, nothing much else is registering.
If I had four cores the script would run at about
half the speed, because it can't be run across 2
threads. For that the script would have to be
running multiple, separate operations. Likewise
with PS. A sharpening routine is a single operation.
You can't spread it across 2 threads or processes.

If you print and go online and have AV scanning
while you're doing the sharpening routine then the
4 cores might be better than 2. But what I'm getting
at is that much of the time, for most people, only
one CPU-demanding operation at a time is happening.

An analogy.... Not a great one, but the best I
can think of right now:

Imagine having a set of measuring cups. If you
have 3 people adding 6 ingredients to a bowl, in
small amounts, they can do it fastest with 6 cups.
If they need to each add, say, 1/4 cup sugar and
1 cup flour to bowls on an assembly line, having
6 8-oz measuring cups will be optimal. But if there's
one person, adding 4 cups flour and 2 cups water,
then 2 32-oz measuring cups will be optimal. (A 32
and a 16 would be best, but I'm trying to keep
this analogous to CPU cores.)

If that one person has 6 8-0z cups then 4 will just
go unused while 2 do the job more slowly. An 8-oz
cup has to be refilled 4 times with each operation.

Since CPU speeds seem to have plateaued in the
3-4 GHz range, there's a limit to the possible speed
of one core. So the question becomes: Do you have
3 people to use your 6 cups? (Do you actually have
frequent, concurrent operations to justify more cores?)
If not then you'll fill your bowls fastest with less cores.