Scan Converter and OS Performance Latency

[Xylo Sesame]

Hey all, I'm new to the world of Mac and have an issue that's puzzling me.

I need to connect my new MBP to a projector via SVideo and run dual (not mirrored) displays for video playback. I'm trying to use an older TView Gold (http://www.focusinfo.com/solutions/catalog.asp?id=151) to convert the VGA via Mini DisplayPort to composite/s-video.

Here's the trouble:
My MBP slows when using the scan converter. I've checked the Activity monitor and don't see anything impacting general performance, but the GUI is like molasses. Windows and dialogues take forever to load, buttons depress after a few milliseconds of actual click, etc. The secondary output video playback is not affected, just any GUI or OS actions on my primary MBP display.

I connect to a VGA or DVI monitor and have no issues at all, even when I set my display output to the same resolution and refresh I used with the scan converter.

I've turned off display switching and auto-dimming and am always on AC power; I don't have Time Machine running, AirPort and BT are turned off, there's nothing starting under my login profile, and I've set my user account to administrate the machine. I've got an i7 with a 512mb 320m.

What gives? Why would (or does) OSX care what I've connected when it's pushing the same resolution and refresh?

Any help is appreciated, this has me pulling out my hair...

 

[Detrius]

Check the logs to see if anything that appears relevant is showing up.

/var/log/system.log
/var/log/kernel.log (10.6-only)

 

[Xylo Sesame]

Check the logs to see if anything that appears relevant is showing up.

A nice bit of light reading last night...

I didn't see anything glaring, but this is from an untrained eye. It does appear as though Parallels loads quite a bit at boot, but I'm not sure how that would impact my specific issues. I'm also corresponding with the application developer of my video application to see if it's on their end.

Is there any reason OSX would perform differently depending on end-output, even if the resolution, refresh, and initial VGA connection are the same? In other words, why would I get different performance if a flat panel monitor were attached as opposed to a composite-only projector? Or am I just perceiving differences in my wholly unscientific observations?