Phono cable - necessary?

... what is considered low capacitance for an IC?

There are no hard and fast thresholds, of course, and the total capacitance of the cable, which is what matters, is directly proportional to its length.  But as a rough rule of thumb, I would consider 20 pf/foot or less to be low, 20 to 40 pf/foot to be medium, and more than 40 pf/foot or so to be highish. 

Blue Jeans LC-1, as you’ve seen, is about 12 pf/foot.

"pf," by the way, is short for picofarads.  1 pf = one trillionth of a farad, a farad being the basic unit of capacitance, although 1 farad represents an **extremely** large amount of capacitance, at least in the context of electronic devices.

Best regards,
-- Al

Chakster, there are many "normal interconnects" that will provide excellent shielding, and can be used successfully in phono applications. Although of course there are others that do not.  For starters, see this recent thread, especially the responses by Atmasphere and Mofimadness, both of whom have exceptionally extensive vinyl experience.

Marek (Actusreus), what the dealer told you is somewhere in the middle ground between a considerable oversimplification and complete nonsense.  And I would suggest that grains of salt be liberally applied to any future recommendations he may provide.

The most basic criteria for a phono cable are good shielding and low capacitance, as Atmasphere indicated in the other thread.  Although as can be seen in that thread there are some who even prefer cables that don’t meet those basic criteria. 

And good shielding and low capacitance can be obtained very inexpensively, witness humble Blue Jeans LC-1 for example, which is excellent in both respects while being nominally intended for use as a line level interconnect.  The ground wire that is often necessary can be implemented separately using ordinary insulated hookup wire of moderate gauge.

I am not necessarily suggesting Blue Jeans, however.  Beyond those basic criteria, as with most cable selection endeavors it comes down to system synergy, the sonic preferences and budgetary preferences of the listener, and trial and error at a variety of price points.

Best regards,
-- Al
 

Is cable capacitance of less consideration when used with a low-impedance MC into low-ish input loads (<1KOhms)?

Yes, it will tend to be less important in that situation than in most others. But it can still be significant because depending on the phono stage reducing the capacitance may allow sound quality to be further improved by increasing the value of the resistive load.  For further explanation see the post by JCarr (Lyra cartridge designer) dated 8-14-2010 11:20am in this thread.

BTW, I should add to my previous comments that there are a few situations in which minimizing cable capacitance will not be optimal.  Those would involve certain moving magnet cartridges that are specified to work best when loaded with high amounts of capacitance, e.g. 400 to 500 pf, especially if the input capacitance of the phono stage (which is often unspecified) is low.

Regards,
-- Al