I have found that synthetics are consumed at double or more the rate of conventional oils. This observation has been consistent across a wide variety of vehicles of all different ages.
That means that if your level does not fall all the way to the Low line between 3K mile oil changes now, you may need to add at least a quart between changes if you switch.
When I was a teenager, the motor on one of our shared family cars (Japanese) was run out of oil and destroyed spectacularly. Why? I decided to treat it to a synthetic oil change, and went away for 3 months. It was driven about 3500 miles in this time, and it ran completely out of oil one day. This car had never needed any oil between changes before. Of course, no one had bothered to check the level in my absence...
My point is that if you switch to synthetics, remember to watch that dipstick very carefully. A slight reduction in wear means nothing if the sump goes dry...
1986 300E 5-Speed 240k mi.