To anyone interested, here is the fix:
(1) Intel's driver update utility said that 220.127.116.119 was the latest driver, and that my drivers were current. The utility was wrong. The latest version of the driver is 18.104.22.1686. You can get that driver here:
(2) Windows 8.1 is supposed to update your drivers as part of installation, including the 22.214.171.1246 driver. Even though it says it has, it does not. Or there is something wrong with the driver version Windows uses. Opinions seem mixed.
In any event, downloading the 126.96.36.1996 driver and running it fixed my problems.
THIS "FIX" IS VERY BUGGY.
Running 188.8.131.529 Windows 8, my RAID 10 worked perfectly and was completely stable.
Running 184.108.40.2066 under Windows 8.1, my RAID 10 is an unstable pile of excrement.
The so-called "upgrade" to Windows 8.1 has been an absolute disaster - one, by the way, that it is impossible to revert from. You cannot simply revert to a previous restore point. The only way to revert safely is to completely clean and reload your computer. Insofar as the only reason I bought Windows 8 in the first place was due to RAID support issues in Windows 7, this is infuriating.
Do ANYONE know ANY way of getting 220.127.116.116 to run stably with Windows 8.1?
A sample of what is happening:
=> Moving files between folders causes Windows to freeze.
=> Rebooting causes Windows to run slowly for a while, and then RST announces that you need to "verify" your RAID.
=> Verifying your RAID essentially makes your computer unusable for 6 hours.
This happens every day.
Never again will I use an Intel RAID on my computer.