Just merge SkS and SpS and either apply job-specific scaling to the resultant consolidated Speed (or buff them to be slightly BiS for the jobs that most favor them and therefore competitive for most jobs) or have it affect them damage of most abilities and periodic damage identically to Determination. As such, all secondaries would affect time-limited damage identically (with Speed simply swapping GCD damage to frequency of GCDs, thereby being more easily balanced across jobs with varying portions of GCD-affected damage).