is about the max flow 2 1" pipes usually carry. It may be tricky with this setup. Going with something smaller may be a good idea in this one instance. Another option could be to drill the top side of the sump so the drain line can enter it unrestricted. That's how I would approach it if possible.
Most large internal pumps simply produce more heat than smaller pumps, whether or not the flow is constricted. It isn't as big of a deal in some areas but where I live heat is a big issue. In Louisiana we're always concerned about heat. An external pump is a good way to deal with that headache.
The overflow style analogy only really works when the tube is filled with water and not air water mix, like in the drain line. Air in the overflow line could possibly stop the flow. That's the concern. The OP may just have to test it out if the sump can't be drilled for the drain.