just as a point of reference, a '72 up sportster supply pump puts out 1 liter/minute @ 1000 pump rpm. I think that's about 3 times what the stock pump does. I did some testing last winter. Let us know what you find out, I never did any testing on return pumping.
Here's a link to my test setup. http://www.freewebs.com/dicky_linn/modi ... typump.htm