the 4x4 pump flows substantially more than the 2wd one
the 4x4 and rs500 pumps flow the same
there was a gpa 2wd pump which flowed more than a std 2wd but not as much as the 4x4 and rs500
you only have to look at the difference in impeller size to see the flow rate differences
a std 2wd cooling system works surprisingly well