I think it's 800 x 600, I don't even get that far as it just rolls and scrolls from the moment I power up the PC.
I noticed the monitor says it can handle up to 60hz resolution so I don't know if I need to change some settings further instead of running Soft15.
I did play with my vertical hold a bit, but it didn't seem to help much, it rolled around up and down with the slightest turn. I also get the dual picture thing I have heard others mention, where a second image appears ghosted to the lower right of another.