Selva 50HP Madeira 684cc MAGNUM Boat Performance Spark Plugs revisited

I wanted to test again Brisk racing spark plugs (NOR14LGS) now that I have upgraded to larger carburetors and lifted the Selva Madeira outboard to the highest mounting position.

I'm comparing against Champion L78 which is one of the recommended spark plug types by Selva owner's manual.

I'm only interested in the top speed gain and after careful testing there was a 0.4 knots difference favoring Brisk spark plugs. This difference is so small that it might be caused by weather, how high the outboard was trimmed and the differences in GPS accuracy.
I also found that my Selva Madeira was not trolling well, the engine stalled many times maybe due to too low RPMs. I raised the idle RPMs to 1200 but when the gear was on the RPMs dropped sometimes below 800 and Brisk spark plugs were not able to keep the engine running. With Champion spark plugs this did not happen.

To sum it up I'm not planning to use these Brisk racing spark plugs because I want the outboard idle and troll properly. Champion spark plugs are also very inexpensive.