What with the mighty Twin Cam 88 (Twinky) mill choking up about 62 anemic horses at full throttle a rider needs all the spark he can get. In my experience the Accel Cyclelite Platinum zappers are far better than anything The Motor Company offers, including the Screamin' Eagle plugs. I can feel the difference at startup and on long hauls through hill country. If there's anything that tops Accels for improved performance I haven't found it.
I have around 39,000 miles on my 2000 Road King and probably 95% of those miles have been clocked with my wife on the back, a King Tour-Pak, Premium Tour-Pak Luggage rack with a Tour-Pak Rack Bag on top of that. We take 2-3 week long trips annually and we are fairly packed to the max. I'm not a small guy and I have used Champion, NGK and Harley's Platinum plugs. I have found these plugs to give the most consistant performance, with the greatest fuel mileage (carb) than the others. I always apply anti-sieze compound and torque the plugs to shop manual specs. For my bike and my applications these plugs work the best for me.