Pete, I found specs in several places indicating that the recommended load capacitance for your cartridge, which is a moving magnet type and is therefore considerably more sensitive to load capacitance than other types, is 150 to 200 pf. I also found an indication that the capacitance of your King Cobra cable is 110 pf/meter, or about 33.5 pf/foot, although that is not necessarily definitive, as it was provided by a user in a forum post. Also, as I mentioned, unfortunately the input capacitance of your phono stage doesn't appear to be specified.
My guess, though, is that if your present King Cobra cable is the same 0.5 meter length that you want for its replacement, the total load capacitance that is presently being presented to the cartridge (by the turntable's internal wiring + the phono cable + the phono stage input) is in the right area. However, if the King Cobra cable is a more typical length, such as 4 or 5 feet, I suspect that the total capacitance being presented to the cartridge is likely to be significantly greater than the recommended maximum of 200 pf, and would therefore probably be contributing to brightness significantly.
In the latter case, just going to a shorter length such as 0.5 meters, even with the same cable type, is likely to help. And even more so if the cable has significantly lower capacitance per unit length, say 10 to 20 pf/foot. However if the King Cobra you are presently using is only 0.5 meters, then capacitance is probably not involved in the issue.