My yard has a high water table (creek, and 4 foot elevation about 4 foot elevation over almost all of the yard), where tree roots often just sit at the surface, so I was wondering how low the water table should be in order to consider something well draining.
Not remotely related. The level of the water table has nothing to do with how well the soil drains.
High water table can be in clay that doesn't drain very well at all, or in a gravel pit that drains exceedingly well.
If you filled a bathtub with each soil and set the water level to 4 inches from the top, it would be the same place for ether type. If you pulled the plug on the bathtub, they would drain very differently.
There are places where you have to drill hundreds or thousands of feet to find water, but the surface turns to a slimy clay mess when it rains.
If your water table is 4 feet down from the surface of the soil, that should be fine for most garden plants. But if you have soil that has a lot of clay, that retains too much moisture for too long, you will have to mix in some sand where you plant your garden.
Most plants don't like feet that are wet all the time. Water logged roots = dead roots = dead plant.
Example: My normal soil is very sandy in most places, so I have to water more often as almost no water is retained there. But I got some potting soil and started some seeds in there in pots, and this soil keeps moist for much longer so I had to water much less or the roots would get diseased from too much moisture.
Does that help?