Need CPU upgrade on new computer? WTH?

[WesW]

Occasionally, when I have battles involving more than a total of 40 units, I receive a message saying that reinforcements which would have normally appeared will not be available because my CPU does not meet requirements.
The auto-detect button set all of the settings to High, though I am playing with Large unit sizes.
The last time it happened, I reduced all graphics settings to the minimum, except for the Bloom and...something else checkmarks, which I didn't notice at the time. It made no difference.

My computer specs:
Model: Dell XPS 410 running Vista Home Premium
Processor: Intel Core 2 Duo E6600 (4MB L2 Cache, 2.40GHz, 1066 FSB)
Memory: 2GB Dual channel DDR2 SDRAM @ 667MHz - 2 DIMMS
Hard drive: 500GB RAID 0 (2x250GB SATA 3Gb/s 7200 RPM HDDs)
Graphics card: 256MB Nvidia GeForce 7900 GS

Are there any guides as to what settings affect performance the most, or anything like a ratio of men to CPU speed (with min settings) to use as a guide? That last battle would have involved about 4300 men total, but I am pretty sure that some of the other times I received the message involved smaller numbers.
Note that there have been plenty of battles involving over 40 units where I have not received the message, even with the video settings on high, so I wonder if there is some kind of hard-coded limit on soldiers for given CPU speeds, and if that limit accounts for dual cores?
Only once have I ever encountered video stuttering, and that was a battle involving two AI reinforcement armies (for three total), plus me.

[sapi]

Edit medeival2.preferences.config and change the line 'unlimited_men_on_battlefield' to equal 1 (or the RTW config, depending on which game you're running)

[WesW]

Edit medeival2.preferences.config and change the line 'unlimited_men_on_battlefield' to equal 1 (or the RTW config, depending on which game you're running)

Wow, that was simple. Thanks! You may want to put this in one of the stickies.

[Slug For A Butt]

Thanks sapi, that's helped me too.