white balance eyedropper, ACR4.1

I use this method.

Search the image at 200% for a gray spot with RGB readings very close to 120 +5/-5 and click my eyedropper on that area. I then preform my adjustments in "fit to screen" mode until I'm satisfied with the image. Then as a final tweek, I repeat step one.

From a technical aspect, is there a problem with my method?

Sounds ok, but very slow. I use presets then tweak them a bit sometimes.

Maybe I'm misreading you chauncey but if the file is RAW then a gray spot could be any number of colours depending on your white balance setting.
The method I tend to use is to click on something you know is white or gray and use that to set your white balance, you can then use those settings for other shots albeit the lighting conditions are the same.
I also have a gray card which works well.

thanks guys, I appreciate the input