"I know some of the differences between the 400 and 200 are,
winglets,
ehanced GPWS,"
Unfortunately, it's not that simple, PH.
For example, Japan Airlines have domestic versions of the 747-400 without winglets... and Qantas, is retrofitting EGPWS on their "Classic" 747's.
As already mentioned, there are just too many differences to list. Different autopilot, fuel system, navigation systems, pneumatics, hydraulics, engine control, flight controls, etc. The 400 has much more automation, and, as a rule, is much easier to fly and fix.
Rgds.
Q.