The testing is done and it yielded some very interesting results.
Testing Method
Basically, the application just adds either 1 + 1 or 1.0 + 1.0 for one second and repeats this 10 times.
Not basic...
1) It starts 8 threads which just add in an endless loop.
2) Once all threads have been started, it zeros all their count from 0 to 8.
3) It does nothing for one second while the threads count.
4) It reads the value of each thread, 0 to 8, and zeros it.
5) It repeats step 2-4 nine times for a total count of 10.
6) It adds up all those scores producing the cumulative score ("[C]") and averages the value for each test ("[0]" through "[9]").
7) Repeat steps 1-6 for doubles (1.0)
8) Repeat steps 1-6 for ulongs (1) but only 4 threads.
9) Repeat steps 1-6 for doubles (1.0) with 4 threads.
The app is a light weight in that the mathematical operations it completes are stupefyingly simple; however, it will load your CPU to 100% with those stupefyingly simple calculations. It's kind of like putting a race horse on a treadmill to see how much distance it can cover in a given time (approximately 10 seconds in our case).
The Results
What Do We Learn From This
1) Does hyperthreading help? Without a doubt. The Core i7 is a lame duck without it's hyperthreading even in the 4-threaded tests that should have matched in both tests. Disabling Hyperthreading, even when you need the capability to run just four threads, is a bad idea.
2) How does the higher clockspeed of the 955/965 stack up to the lower clockspeed of the 920 in sheer counting prowess? Not well. Core i7 920, with or without hyperthreading, is clearly faster clock for clock. The Phenom II 955 has the lowest counts/clockspeed ratio of those tested.
3) How does the actual work output compare to the power consumption? This is a guesstimate based on TDP which Intel and AMD measure differently so take with a significant portion of salt. Core i7 920 w/ Hyperthreading is the most efficient with the dual Xeons being last. The Phenom II 955 makes a relatively strong showing here.
4) How does the 955/965 fair compared to the 920 at running 8 vs 4 threads? First, it is surprising to note that all platforms tested did worse with 8 threads versus 4, even a dual Xeon quad core platform. This discovery baffles me. Even then, as expected, the dual Xeons had the least decline in performance going from 4 threads to eight while the Phenom II pulls up the rear. The Core i7 takes a huge loss in this department with Hyperthreading disabled.
Conclusion
In this simple test, Core i7 920 w/ Hyperthreading enabled sweeps the floor of all other processors tested except in comparing 8 threads to 4 threads (dual Xeon saw the smallest loss). If you have a Core i# with Hyperthreading, do not disable it.