I'm not sure we've established this in a clear cut way. For a given individual the stronger they are the faster they will be, at the same skill level. Now, the relationship between muscle mass and strength is a bit complicated, but in general, the more muscle a person has the stronger they are. One exception to this is when the individual is over training or injured and those muscles aren't healthy or something of that sort. There may be other exceptions but I can't think of any right now.
There are individuals who are extreme genetic outliers that may get slower once they achieve extremely large muscles, but that isn't me and it probably isn't you or anyone else reading this either. There are also extremely specialized sports, like running marathons, where weight of any kind is detrimental and strength is of little to no benefit (for the sport, it's still of great benefit for daily life).
Notice I'm only comparing individuals to themselves. There may very well be people who, due to variations in muscle fiber type distribution and other genetic factors, are stronger at a smaller size than other, more muscular people. These people would be stronger still if they carried more muscle.