I've used two SpeedLock firing pins in the past couple of years and have replaced both of them because of misfires. One of those misfires was expensive.
The problem with the misfires I experienced were due to a lack of energy applied to the primers. By this I mean the light weight pin coupled with a relatively weak spring didn't have enough energy to cause the primer to fire. The spring that was supplied with the SpeedLock had a similar compression weight to the original stock spring.
If one has a Speed Lock pin or any other lightweight firing pin, one is able to demonstrate for themselves just how soft the lightweight pin strike is by seating a live primer in a case (NO POWDER OR BULLET! ) take it outside and fire it. Do the same exercise with the stock firing pin with the SAME spring, There should be a noticeable difference.
The pin protrusion on both my rifles (Rem 700's) were .051" (a .223) and .054" (a 7RM). On the 'misfired' primers, one should notice the 'dent' made by the strike isn't very deep; at least mine were not. When these pins did fire the round, I also had a cratered primer with a deep pin strike regardless of the load. The crater was due to the fact that the diameter of the pin was several thou smaller than the bore in the bolt face. Additionally, the fired primers always looked like a good strike (other than the crater ring) because the force of the detonated powder charge would drive the case back against the bolt face and the protruding firing pin.
My solution was to use a Holland's oversize pin and a heavier spring. Fitting the Holland spring solved the cratering issue. And the heavier spring makes sure the primer is struck with authority. Both rifles have gone bang every time since this change.
As for the difference in lock time, in my opinion, good shooting form will out weigh any disadvantage the heavier pin may cause.
I used to blame these misfires on bad primers. I've since proven this is not the case. I found a few of those primers in my scrap bucket and tried to re-fire them as described above; all detonated.
As for the expensive mis-fire I mentioned earlier. I made tag soup out of a hunt I went on a couple years ago. On the last day of the hunt, pulled the trigger, gun went click, deer moved out of position and never came back. Drove from Wyoming to NY dreaming of the tag in the cooler.
The lightweight pins may have a place in a competition rifle but they don't have a place in my hunting guns. MHO
Pete