not all the time, the 805 CPU i was talking about is a Good Budget Chip- Smithfield (2x Prescotts) Chip, Pressler is the 65nm cpu that runs cooler than Smithfield, and overclocks higher, Considering Intel Came out with Dual Core, Hyper Threading is not needed AFAIK, it was a good feature back during the P4 Northwoods.
HT was the beginnings of Thinking of Dual Core CPUs, I have it enabled on Mine cause it does tend to make things run alot smoother when running multiple Apps, like Webbrowsers, IMs, etc there is only 1 game on my system that whines a little when i try to run other apps on 1 part of the CPU, that is due to it comming out in 1996.
I had that very same 2.66ghz 533fsb northwood w/out HT socket 478 as you in my past system. I can definately tell the difference with my current 650 3.4ghz HT. But..... on the other hand... it could be that the 650 is faster both cpu speed and fsb plus the larger cache. hehehe... Now on the other hand.... I have tested in my own measley way to see if the HT was working.... I did a ctl alt delete to get the performance panel displayed showing the two graphs for cpu usage ( one is core and one is virtual ).... ran PI and had a couple of web browser open at the same time.... the graph shows one was 100% while the other was going up and down depending what I was doing with the web browser.... well at least for me that was how it was displayed. guess HT was working...
Yeah my office PC, which is a Dell 8400 not a self built one, has a Pentium 4 540 Prescott w/HT (3.2Ghz), and its faster than my Pentium 4 Northwood @ 3.26Ghz. The Prescott 540 is running 60mhz slower than my Northwood but yest its faster but I think thats due to the fact that the Prescott core is just a faster design than the Northwood core not because of HT. Not saying HT is bad, it certainly helps, but it aint revolutionary.
I have a different results with your northwood vs precott thing.
I was lucky enough to find a 3.2ghz 800fsb 512K cache Northwood with HT in a socket 478. it is in my wifes machine and it runs great. when I run benchies that are cpu based on her machine vs mine.... both are very comparable to each other sans a few points lower due to a couple hundred mhz lower on her machine. I take into account the differences in gpu's.... her cpu runs along mine except the fore mention mhz differences.
 i just ran Super PI on both system. my wife's Northwood 3.2ghz 800fsb 512k cache ran 1M PI in 44sec. vs my Prescott 3.4ghz 800fsb 2mb cache ran 1M PI in 37sec. so would increasing the Northwood by "200mhz" to 3.4ghz make up the difference ?
Not by much...... well at least not with the 600 series of Prescotts. Currently with the weather this time of year.... my system is running at 29C idle and around 40 load with a Zalman 9500 cooler and my wife's Northwood is idling at 26C and around 38 load with a Zalman 7000 cooler according to both motherboards sensors. Both are in very small cases, a desktop (mine) and mid SFF (wife's) both having much more challenging conditions when compared to a mid to full size tower in itself. You have see both mine and wife's system pictures (link to pictures in sig). Now in the winter time... both systems run much cooler.
So... you really cant brush stroke all Prescotts run hot. Maybe the earlier versions as in the Prescott socket 478 to the early 500 series... but the 600 series does very well.