one of my rod building buds sent me a web site for published data that says the TFO rods are typically underweighted by 2- 2.5 line weights, meaning it might take a 6 or or 7 weight line to make a 4 weight rod sing. if I find the table of data again, i'll publish it, but it may be googleable.

interestingly, TFO's two handed rods show no such underweighting; the published line weight windows for them seem pretty close