The DR8EA plugs work great, the D8ea plugs (non resistor) work great also, as the plug leads have resistors in them already. (I do not have any bike mounted audio system, so I do not know if the non resistor plugs hurt the radio sound. I have a set of Nippondenso HOT"U" X24 that have been in the bike for 24,000 miles and they still rev freely all the way to redline.
When I thought I had spark plug trouble, I pulled the plugs and they looked fine, it turned out to be the plug wires. I do not think this water cooled engine is very picky about spark plugs. Some old air cooled bikes could glaze up the plugs in one hot afternoon on mountain roads