It looks like your Merlin are 8ohm nominal, going down not lower than 6.5 ohm... An easy load. So you may not benefit from the lower resistance of a mega large wire like the classic 6.0, unless your length requires it.
With the ply 3.4, you have more than adequate awg and you have a lower inductance than the classic because of the cable construction... I would stick with the ply, it looks like it is the better cable, but hey classic 6 is less than $4 a foot, so it may be worth the try, and your sound will possibly change if that’s what you are looking for.