50 miles/day isn't so much, but it depends on how much you're carrying. If you are staying in hotels/motels and don't need sleeping gear it is pretty easy at a steady pace. If you are carrying everything like the OP, it is a little harder as that stuff adds a lot of weight, but it is still doable.

But here's some different advice: If you only have 20 days, and you won't have much time in NYC anyway, "Go West Young Man".