17" Running on Battery (big performance decrease)

I have the most recent 17" Matte Unibody with a 2.93 ghz, 4gb ram, 7200 320gb hard drive.

I noticed something very annoying last night on the plane. I was running an action in Illustrator to save pdf files at the lowest resolution and quality. I normally do this by running the batch mode, but I noticed it was taking 20 seconds per file. It is usually instantly that it can perform this action. Every once in a while it would perform the action at the normal instant speed, but 95 % of the pages were taking about 20 seconds. I then followed stopped the batch and tried manually doing single page saves from my action and got the same results.

So I decided to log out and log back in under "better performance". I unchecked all of the options to save battery life and didn't have the screen saver or screen dimmer set. I even restarted the computer. Still the same slow results. I get home, all of the above actions listed with my computer plugged in and I was back to full speed.

Am I missing some kind of performance option in the energy saver options?
I remember on Tiger that you could pick "better battery life" and "better performance." Is that not in Leopard.

Does any one have any idea what could be causing this sluggish performance? I also did a repair disk permissions, ran the verify disk, set the hard drive to never go to sleep, check the activity monitor and didn't notice anything big going on behind the scenes. I just had Illustrator CS4 open. I also reset the Pram.

Thanks!

I read that other thread... but this is a very noticeable difference. We are talking about 20 seconds vs. less than 1 second when plugged in to perform a simple task.

I just wonder if it is more prominent in specific tasks or if it is an Adobe CS4 thing. I have been have lots of performance issues while plugged in with CS4 Photoshop. The only odd thing here is that the same task that I do in Illustrator plugged in and not plugged are like night and day as far as speed is concerned and every once in a while (about every 1 in 40 pages) the action would work at the plugged in speed.