Reason for this is people seem to keep asking the same questions over and over again. There are multiple answers. But the simplest one is..

HT:on will considerably improve your performance ONLY IN windows 7!


http://www.nire.com/2009/05/core-i7-hyper-threading-off-part2/
I have translated this for you guys.

"Its rumor that having HT:on will make PCs go faster. I have setup 3 similar rigs with differing OS. I have found that the improvement is very much OS dependent."

PCMark Vantage



"As you can see having windows 64bit HT off has a considerable performance improvement, but Windows 7 64bit HT:on is by far the best. Could this just be an error in vantage? So i decided to try it with XP too!"

3DMark06



"HUGE DIFFERENCE! HT off on xp is undoubtedly the way to go! Next is the FFXI benchmark"

Final Fantasy XI Benchmark



"The graph looks very similar to the vantage and 3dmark06 scores. Having the right OS with the right platform is in fact important!"

The Last Remnant



"Strangely enough we see the same graph in thi benchmark as well!"

CONCLUSION
"So in conclusion, HT on/off can indeed vary with the OS in terms of performance.

Windows XP 32bit - Turn HT off for better performance. 27% difference in benchmarks.

Windows vista 64bit - Having HT off is better for performance. but can vary with the program used if optimised for HT.

Windows 7 64bit - DEFINITELY TURN HT ON!!! it is simply on a different level."


OH! And heres the nail in the coffin for vista 64bit

Conclusions (VISTA Ultimate 64Bit tests) - excerpt from ixbtlabs review


http://img.techpowerup.org/090729/ixbitconclude531.jpg

Why on earth would you turn HT on and forego a higher OC for "that" much gain..
Turbo is great.. but HT... come on now... lets think practically for a moment...
4.2ghz HT off.... or 3.8ghz HT on in vista 64bit. You tell me which you like.

I hope this helps answer questions on HT.

Following is another link to back up the above mentioned data
http://ixbtlabs.com/articles3/cpu/ci7-turbo-ht-p2.html

and finally temps..

- Idle temps an vary, but very little with HT on/off
- Load temps will see anywher efrom 8-11c cooler temps with HT off!

Hope you enjoyed the read. And this puts a rest to the clone threads on HT.

And now for a screen of my temps with the rig below
4.2ghz OC 201qpi HT on Turbo on noctua NH U12P pushpull air cooling
linX 5 run stable... 60gflops.. holY!!! lol never got that high in vista...


http://img.techpowerup.org/090728/linx4-2ghz.jpg

bump cuz someone asked to.

can we PLEASE get a benchmark on Linux OSes with/without HT?

mikotan you have just reinforced my decision today to turn off HT. If you look at that violet graph you see it says there is no significant diff. The other winning numbers in Win7 are just benchmarks, and are not significant differences. It is the real-world use that I am interested in, I am not trying to impress anyone with benchmarks.

This was a result of my post here:

Re:Need Advice with HT or without HT and turbo - Post #2

mikotan

Reason for this is people seem to keep asking the same questions over and over again. There are multiple answers. But the simplest one is..

HT:on will considerably improve your performance ONLY IN windows 7!


http://www.nire.com/2009/05/core-i7-hyper-threading-off-part2/
I have translated this for you guys.

"Its rumor that having HT:on will make PCs go faster. I have setup 3 similar rigs with differing OS. I have found that the improvement is very much OS dependent."

PCMark Vantage



"As you can see having windows 64bit HT off has a considerable performance improvement, but Windows 7 64bit HT:on is by far the best. Could this just be an error in vantage? So i decided to try it with XP too!"

3DMark06



"HUGE DIFFERENCE! HT off on xp is undoubtedly the way to go! Next is the FFXI benchmark"

Final Fantasy XI Benchmark



"The graph looks very similar to the vantage and 3dmark06 scores. Having the right OS with the right platform is in fact important!"

The Last Remnant



"Strangely enough we see the same graph in thi benchmark as well!"

CONCLUSION
"So in conclusion, HT on/off can indeed vary with the OS in terms of performance.

Windows XP 32bit - Turn HT off for better performance. 27% difference in benchmarks.

Windows vista 64bit - Having HT off is better for performance. but can vary with the program used if optimised for HT.

Windows 7 64bit - DEFINITELY TURN HT ON!!! it is simply on a different level."


OH! And heres the nail in the coffin for vista 64bit

Conclusions (VISTA Ultimate 64Bit tests) - excerpt from ixbtlabs review


http://img.techpowerup.org/090729/ixbitconclude531.jpg

Why on earth would you turn HT on and forego a higher OC for "that" much gain..
Turbo is great.. but HT... come on now... lets think practically for a moment...
4.2ghz HT off.... or 3.8ghz HT on in vista 64bit. You tell me which you like.

I hope this helps answer questions on HT.

Following is another link to back up the above mentioned data
http://ixbtlabs.com/articles3/cpu/ci7-turbo-ht-p2.html

and finally temps..

- Idle temps an vary, but very little with HT on/off
- Load temps will see anywher efrom 8-11c cooler temps with HT off!

Hope you enjoyed the read. And this puts a rest to the clone threads on HT.

And now for a screen of my temps with the rig below
4.2ghz OC 201qpi HT on Turbo on noctua NH U12P pushpull air cooling
linX 5 run stable... 60gflops.. holY!!! lol never got that high in vista...


http://img.techpowerup.org/090728/linx4-2ghz.jpg

HT is not on. You would'nt be getting 60 GFlops with HT ON at 4.2ghz. Also Linx shows only 4 threads down at the bottom. With 86c maximum temp I dont think you should be turning HT on at 4.2ghz