Why exactly is this? None of the parts stores in my city (or vancouver) had non-resistor caps. They said resistor plugs with resistor caps is no problem??
If your plug wires or the insulation in your coils are weak, you may have sparks going to ground before the plugs. "May have" are the words to note. If everything is in good order, you will have a hot spark.
I run resistor caps and plugs without issue to 10,000 RPM on my DOHC with TCI ignition. Plenty of hot sparks.