If you want to get really cheeky, create multistage missiles, where the second salvo catches up to the first, which then unloads the submunitions to pace the second one, only to be reached in time for target by a faster third.
Given that targets with high shield regeneration, but very slow speed are rare, I can only think of one ship that description fits to.
In this case, I suggest getting higher tech.
Long ranged beam weapons might be a solution, as are smaller sized launchers.
And movement will probably be pretty predictable.
The missile storm tactic did exist in the past, read Steve's TN Campaign to see an example of that.
Which was more or less also the reason it got dropped.