IP is plate current , Gm is transconductance .
In your Mid Monos you need matched tubes unless they are the latest version with a trim pot for each tube’s bias.
Bob only has three matched tubes.... if you put one that isn’t close then one amp will have a tube that is not biased correctly because the two power tubes share a bias pot . One will draw more current than the other , not what you want in a Push / Pull amp.
IP plate current is what you are adjusting. It’s basically a math formula that relates to the plate voltage and how much current the tube will / should draw
Your amp has a plate voltage of something like 440 volts. Mike at Quicksilver recommends setting the bias at 53 mA.
You can’t achieve that if both tubes are not electrically " the same" with respect to their current draw. . Quicksilver strongly recommends matched power tubes for best and safe operation.
When you buy a QS product new the tubes are hand matched on their equipment and are very tightly matched. Looking at a pair of EL84 and the current draw is hand written on each box. 24.1 and 24.0. That’s how tightly matched they should be. Those were from their Headphone amp that has no adjustment, it’s Auto Bias so technically they don’t need to be matched . But they do it on all of their amps
Transconductance or Gm is how strong the tube’s emissions are .