Hi Carl,
Long story! We're trying to produce an animation from a model running in a simulation engine. It throws out events (state changes which we would convert to tweens) in a long list which we then feed into a timeline to do a post-simulation playback visualization. Its all part of a spike to see if we could display results of the simulation online.
It seems that once the timeline is processed/created, playback control is effortless so if we can figure out how to speed that up, GSAP would be a good option for us.
Happy to share more details offline