What is the most crucial factor taxing performance?

[Quietus]

Personally, it's Unit detail. When I put it to "very high", the game slows down. On "high" everything is manageable.

Kraellin says AA too, so I keep it down to 2x. Actually, I had it to 4x not realizing it was the Unit detail that is making the game drag.

Have you updated your drivers btw?

I only use 1024x768 since I don't know how to mod the auto optimisation file to 1280x800. I'd say start with the unit detail then the resolution (but since your unit detail is already "high", start with the resolution). I'm surprised your machine is slowing down so easily.

[The Stranger]

go to preferences.txt and look at graphics replace 1024x768 to 1280x800

[BDC]

go to preferences.txt and look at graphics replace 1024x768 to 1280x800

It isn't that easy (well wasn't for me), there is a file with what it thinks is the best your computer can manage, and you might need to edit that too...

Don't know what CA were thinking with that. If I pay for a game, I expect to be able to run it at the resolution of my monitor without hacking some text files.

[Someone Stupid]

What do you have running in the background - in the system tray and also how many processes are generally running in the background?

I'd try to stay at the resolution your at, LCDs generally don't look too nice out of their native resolution, but I'm sure you knew that. Still, if there is no scaling for screen size (I don't think there is), this is probably as big as or bigger than AA - see my comments below for details on it.

As for what what takes the biggest hit power wise:

AA or Unit Size (one is entirely GPU dependant, the other is a bit of both)
Unit Details
Shadows
Sound
Terrain Detail

That isn't set in stone and one can have an effect on the other (AA most likely always be at the top). Unit Details and Shadows will swap depending on setup, same with sound and terrain details. If your using onboard sound I'd imagine it eats up more where it hurts (at least on larger unit sizes) than terrain details do.

Minimal UI isn't helping since you are showing more of the screen - thus that factor could be next to nothing if it is just showing terrain to being huge hit since you have an extra 1/5th of data having to be rendered. Thus it could be at the top of the list or the bottom of the list. Still, the other aforementioned settings wil determine the effect a minimal UI has.

Screen size makes some difference, although unless you go markedly down or up it won't be much - the game only supports the basic resolutions so your drops are going to be big anyhow. Dropping to 1024x768 would be noticeable since it doesn't seem to scale to keep the same FOV. So that would leave you with a smaller FOV which means less overhead associated with anything on the screen as less is to be drawn in more ways than just pixel count.

Remember though that irregardless of card, you need processing power as you go up in unit size. Your card can't render what it doesn't have the basic data for. Two units colliding results in added CPU overhead because now it isn't just providing basic plot data and AI, it is also calculating attack/defense and other combat values and it is having to calculate a lot of them - including those that aren't on the screen. Not to mention added sound overlays if you haven't reached the game limit, and if you have, it will then have to decipher which ones to play and which not to - and the more it has to choose from, the longer that takes.

If your really looking to up performance after playing with settings, I'd try several sets of nvidia drivers (try for one that is about a year old, then a 6 month old driver, and also the latest driver - you might want to set up a custom battle that you know will unfold relatively the same each time with FRAPs running to get the average FPS if you want to find the best set) as compatibility and playability are known to change dramtically in some games between different sets. I'm not sure if this is one of them, but a driver swap isn't hard to do. I'd D/L the latest drivers first though. Background applications/processes can make a huge impact as well - so if you don't need it, eliminate it.