I generally use 2x and 2.5x power. I have 3x and higher, but the working distance (focal distance) becomes shorter and shorter the higher the magnification. This means it's harder to get a comfortable working position and keep the handles from your paint brushes from hitting against your face or magnifiers.
Basically, if you don't have enough room for your tools or the amount of depth perception is too shallow, switch to a lower power until you're good.
You don't say, but I assume that you're using a binocular magnifier (has lenses for each eye) and not one of those single lens desk lamps.
If you are using one of the single lens magnifiers (desk lamp or on a stand), switch to a binocular headset or reading glasses. The binocular vision gives you the depth perception you need for modeling tasks. The single lens devices are OK for inspection work (checking out your stamp collection, or whatever), but they're not very good to work under.
Happy modeling!