Update!: Gigabyte personally issued me a fix for my P35-DS4 board: BIOS version F13b. I understand the "b" is beta, and not an official version. Just to recap, I have the GA-P35-DS4 revision 2.1 with an Intel Q9450 2.66GHz Yorkfield CPU.
Their words:
"Attached special bios is modified to support Q9450 and also keeping bios codes from F5 bios to avoid DPC issue."
It appears to be similar to what some other people have also been given by them.
Benchmarks. This is my previous XP 32-bit BIOS version F12:-
New XP 32-bit BIOS version F13b:
Anything from 4 microseconds to 22 at idle. I get an occasion lone spike at 129 microseconds every 15 seconds or so. But the average toggles between 5 and 12 microseconds.
I used a hard-wired PS/2 mouse for the above screengrab. My Microsoft wireless optical mouse was taking the latencies anything up to 42 microseconds whenever I moved it, but switching to a hardwired PS/2 mouse cut these latencies by half.
Now on to Vista-64...
This is what I was getting using BIOS F12 in Vista64 after a clean install (with chipset and graphics drivers only. I haven't updated Vista-64 via Microsoft Update yet, because Vista wont "see" my ruddy USB Modem even though the modem has genuine 64-bit drivers! Gah!):
... basically a mirror image of what was seen in XP-32.
Opening a few windows sent it wappy, though:
Now Vista64 with new BIOS version F13b:-
When it's all settled down (there's absolutely loads of spikes when the OS has first loaded up), and without optimising anything other than disabling ethernet, I get average of 59 microseconds. It oscillates tightly between 57 and 60 microseconds, apart from random spikes (anything up to 5000 microseconds):
Disabling Aero barely affected the values. However I went the whole hog and disabled ALL fancy frills, setting processor scheduling to Background services, etc., but then...
.. Disabling my Samsung SH-S203P DVD-RW drive (via Device Manager) took the average down to 29 microseconds:
Still get spikes when changing windows and stuff, though:
... these can be anything up to 5000 microseconds, as mentioned, and can last a second or two.
But still pretty surprised Vista got down that far, on the whole. I haven't even updated it yet, or installed SP1, etc.
All my tests/screegrabs were when the systems (XP-32 and Vista-64) were IDLE. I don't have any projects to test it as yet, as up until now I've generally been more hardware based, with a little bit of software. I can now work to integrating all my hardware with my computer, and get my hands more dirty with the software side of things.
Thanks for all the help, anyhow. Have thankfully cancelled my RMA request.