I took a look at the OCOS description. While I have no reason to question its being an excellent choice for longer runs (and at $1K for 7.5 meters it had better be!), I find the design rationale offered there to be, um, unpersuasive and incomplete.
There is no indication of inductance, capacitance, or resistance. The terms "characteristic impedance" and "impedance" are used interchangeably, when in fact they are very different. "Characteristic impedance" is a transmission line concept, which only comes into play when cable length is a significant fraction of a wavelength. That is not even remotely the case at bass frequencies for a 50 foot cable. Which makes the graph included in their literature meaningless.
The "impedance," on the other hand, that would result from the inductance of a 100 foot round-trip run of speaker cable certainly can be expected to be significant in relation to the nominally 4 ohm speaker impedance (which is undoubtedly even lower at some frequencies). But the OCOS' inductance is not specified.
Again, while these cables may very well be excellent choices for longer runs, aside perhaps from their cost, their technical rationale is unpersuasive, and the technical information provided is not complete enough to allow a meaningful prediction of the compromises that a 50 foot run will result in, compared to a shorter run.
Regards,
-- Al