Assassin's Creed (PC) FPS issues. Any ideas?

Processor: Intel Core2 Quad Q9300
Graphics Card: ATI HD 4870 1GB Memory
Memory: 4 GB RAM
Motherboard: ASUS P5N-D
Operating System: Windows Vista Business SP1
AC Version: 1.02 (Newest Patch)

(not sure what else you're going to need there...)

I don't know why, but I'm getting about 24 fps during random intervals whenever I'm in a densely populated area. While I do have everything at max settings (Multisampling set to 2, not 3)...I have tried the settings at other varied settings (from lowest to medium to highest). I only run the game at 1024x768 @ 85 Hz---I've tried with and without v-sync, and I have tried it in DirectX 9 and DirectX 10, both with the same settings being tweaked to see. As expected, the game runs slightly worse in DirectX 9, but it doesn't change the fact that my hardware should not be having issues (as far as I know) at all with this game.

Yes, yes, I know the usual suggestions: I've uninstalled and reinstalled the latest drivers for my graphics card. I've got my motherboard's chipset drivers installed correctly. There are no other programs running in the background. I've tried to run in compatibility mode for XP. I run the program as an Administrator.

The game runs AMAZING 85% of the time. But that 15% is SO noticeable. Sometimes the frame rate drops in an environment I wouldn't personally deem "demanding".

Any advanced ideas, tips, and suggestions would be great.

Well if you have tried altering the graphics settings with no avail then it would suggest you CPU is bottlenecking the game. The developers did say before the game was released it would benefit on computer that have higher clock rates rather then PC's fitted with the latest video cards (SLI and crossfire apparently makes little different to the frame rate in this game).

In this you should look for options that will allow you reduce things like draw distance, NPC density i.e. how many AI NPC's are on the screen at anyone time, etc.

lovely