Just trying to think back to the old DSL plans and tcp acknowledgements flooding the upload limit - does anyone remember if I am correct.   

An old DSL plan which allowed a Max down / 128k up speed, would allow you an actual maximum tcp download speed of about 4mbits even if the modem sync'd at a faster download speed. 

Does that ratio sound correct to you?

I seem to remember it being a thing at some point when the max down plans became avaliable.