I don't really trust the published numbers, when they are even published at all. The reason is, flow rate under what conditions? T-stat open, T-stat closed, long rad hoses, short rad hoses, etc. All that changes flow rates.
May years ago in an attempt to fix a low speed overheating problem in my POS sqaurebody trail truck I bought a high flow mechanical pump. The stock GM pump flowed about 41 gpm free flow (using a bucket to test) and the new pump flowed about 50 mayb 51 GPM. Spinning it at 3100 RPM which is the fastest I could easily turn it hanging off the side of a bucket with a hose on it for the test. Obviously this is going to flow less when mounted to engine but in this case I wasn't concerned with the actual number so much as comparing one pump vs the "high flow" version to make sure it was moving more coolant.
Not exactly apples to apples, but an mechanicl FE water pump is going to be reasonably close.
The electric pumps would be easier to test with the bucket method and eliminates the speed variable since they have their own built in motor!