Depending on the firearm desired....
All around for pure speed and reliability I would build a late Manton from castings. This would be great on late flint gun.
If I were buying a lock I would buy something with a toggle link to the tumbler.
Next would be a small Siler. Its very fast if set up right.
If you are after speed forget set triggers, they slow the process since the triggers also have a "lock time".
BUT it is often possible for many to shoot better with DST unless the lock and trigger are tuned for a very light pull.
Jarring the gun.
Large locks jar the gun more. I have a L&R "Manton/Bailes" on a pistol and while it needed some work it now has a really nice trigger and does not jar the pistol at all. I should have this shooting in a week or so if I stop killing time on web sites
Stiff springs, light parts = fast lock that moves the gun little if at all, proper tuning, if it needs it, puts the sparks in the pan. Good vent added to this makes a fast flintlock.
Stiff springs only break flints if the geometry is wrong.
Dan