The GPs have been going 20 years, there were 60-ish years of speedway before that. It suggests if you're naming a top 20 that the GP era should have about 5 riders. We have had Trick, Crump, Nicki and Greg who would all make top 20 and Hans Nielsen ride 5 seasons of GPs too.
By the end of next season Woffy may have won 3 world titles by the age of 25 and in 5 attempts putting him in the top 5!
Who would you say are the top 20 overall?