I don't think there is a rule of thumb. In general, if the speaker cables have a major impact on the sound then I would be more concerned about the amplifier design, how the speaker load varies with frequency and the way the two match...just my two cents.
tube amps/low capacitance cables?
The owner's manual for my 35w p/p tube amp recommends low capacitance speaker cables - but, it doesn't say why. On my two way monitors, I've been using TG Audio HSR silver cables which had been delivering authoritative bass in my former SS amp set-up. But, with the tube amp, the bass is now very weak. So, I'm assuming that these HSR cables are high capacitance, low inductance. I swapped in a pair of Speltz non-twisted anti-cables(low capacitance) and the bass returned. Since assuming can be a dangerous thing, can anyone elaborate about low capacitance cables working better (or not) with tube amps?