Space at my apartment is limited so loops and verticals are the norm but I do have a window of opportunity to shoot an end fed across the property to a tower.
It’s 30M (100′) away and a far stealthier, easier and cost effective choice over a massive vertical.
My question is, with RX antennas does there reach a point of saturation where after the longer you go it will make no difference to pulling signals?
There are so many variables with random wires it’s hard to say. Generally, the longer the wire, the better it will be at low frequencies. The effect at higher frequencies is harder to predict as the radiation pattern will change drastically with frequency. Really, the trick nowadays is to minimise noise rather than chase more signal, which is why more people are going for loops rather than wires.