Those results look pretty close to Fast Fates testing.
http://www.overclock.net/forum/22568401-post7.html
He got up to around 2GPM with a single pump. The minimum is harder to tell because he used a tap to lower flow rather than lowering pump speed but it seems perfectly reasonable.
My loop, A CPU, GPU, MPS400 and dual rad loop runs at 4,6Lpm / 275L/h max flow with a single D5 USB. Older blocks were much more restrictive but these days over 200L/h is pretty common