I took a look at the files.
Heroes of Might and Magic 5\Heroes 5 - Tribes Of The East\profiles\default_profile
user_a2.cfg
....
I'll try checking and tweaking many files, and I'll let you know if anything comes up. You try it too.

I don't think that editing the configuration files will fundamentally fix the AI slowdown issue.
I suspect that the problem lies in the flawed logic embedded in the game by lazy programmers, or added at the request of Intel and AMD to encourage users to upgrade their hardware more often. :)
We need to remove code snippets from the source code that look like this:

//========================================================
// generated by our sponsors, Intel Corp and AMD Corp, please do not modify
//========================================================
for (int i=0, j=random()*time(); i < j; i++)
{
int nFreq = GetCurrentProcFreq();
int nSleepTime = 5000 / nFreq;
sleep(nSleepTime);
}