lack of quantifications is the biggest DBZ problem. i think i can provide a minimum quantification to DBZ reflex speed. and i won't use PL which is debatable that provide proportional speed as it do to raw power, i will go only by feats of speedblitz.
the speed of sight is 0.05 second, if someone can speedblitz a normal human his time reaction will be at least 0.05 second and i say at least, because that's the minimum time frame of an eye to perceive something.
the quickest kick ever recorded until now has time reaction of 0.3 second. that means that the quickest kick of a normal human is 6 times slower than sight. if someone has to blitz a normal human he should be 6 times faster than normal to achieve the least least speed for a kick blitz.
my calculations will be based on direct feats and no powerscaling, no PL and no hyperbols, just canon feats, but my calculations won't give the right speed of DBZ characters, it will give a speed less than the real speed of DBZ characters, but at least it's better to have a minimum cantification to be based on, than actual assumptions. as i said my calculation will give speed less than DBZ real speed, because of those points :
- i will be based only on speedblitz feats, but DBZ speed growth has also happened in other feats where there is no blitz.
- i will be using the lowest speed of blitz, which is the limit of time frame sight.
- i will be using the speed of a kick which is normally faster than jumping, running and moving entire body that is necessary for speedblitz
okey, now we know, as i explained, that for someone to blitz o normal person he must be faster than his sight, meaning he should be 6 times faster normal human. if character A can blitz character B, that means at least A is 6 times faster than B. that means if B has time reaction of 0.3 second, A will have time reaction of 0.05 second, if character C can blitz A, then C has time reaction of 0.05 / 6 = 0.008333 second.
now let's start by Krilin and Roshi, they showed impressive feat of time reaction, where in 1 second, they moved several steps, exchanged sevral punches and kicks, exchanged words, and stopped to think for 1/5 second, it would be save to estimate their time reaction at 0.01 second.
Roshi was able after that to blitz Krilin, that makes him have time reaction at least of 0.001666 second.
at 22nd Budokai, Goku moved so fast Roshi couldn't see him, that makes Goku have at least time reaction of 0.00027777 second
Ten Chin Han who was equal to Goku at 22nd Budokai in speed, was not able to see Goku's movement at King Piccolo saga. that makes Goku has at least time reaction of 0.00004269 second
Yet even this Goku was too slow to even touch mr Popo, and mr Popo was so fast Goku was unable to see his movements. that makes Mr. Popo at least with time reaction of 7.716x10^(-6) second
23rd budokai Goku and Piccolo were so fast not even Kami who is much faster than Popo was able to see them. that means Goku and Piccolo had time reaction better than 1.286x10^(-6) second
Raditz was blitzing both Goku and Piccolo at the beginning of DBZ. that make Raditz with time reaction better than 2.1433x10^(-7) second
Nappa was much faster than Raditz, but Goku after King Kai's training was able easily to blitz Nappa, that makes Goku without Kaioken has time reaction better than 3.5722x10^(-8) second
Vegeta who surpassed Goku's speed without Kaioken, after he recovered from his fight with Goku, had became faster, but was easily blitzed by Burter. that makes Burter have time reaction better than 5.9537x10^(-9) second
Goku who was training under 100G gravity became so fast, that even without kaioken, he easily blitzed Burter. that make Goku have time reaction better than 9.90229x10^(-10) second
Piccolo after King Kai's training and Nail's power up, had become at least as equal as Goku. when he fought 3rd form Frieza, Piccolo stated that his speciality is speed, and Goku stated he can't beat Freiza at that level with his initial Namek level. and Frieza blitzed Piccolo, that makes 3rd form Frieza have time reaction better than 1.6538x10^(-10) second
Gohan matched Frieza in power and speed after getting angry, but he and all the others including Vegeta (who powered up again and became the strongest of them), were blitzed by Frieza 4th and final form, that makes Frieza at final from have time reaction better than 2.7563x10^(-11) second
Trunks moved so fast to dodge Frieza's attack, Frieza didn't see him getting behind him far a way on a hill. that makes Tranks have time reaction better than 4.59393x10^(-12) second
Android 17 is stronger than Trunks, and was blitzed by Imperfect Cell, that makes Imperfet Cell have time reaction better than 7.6565x10^(-13) second
now, skipping to gohan vs perfect Cell, Gohan was able to blitz Perfect Cell easily, that makes Gohan at SSJ2 have time reaction better than 1.27609x10^(-13) second
so just at the end of Cell Saga, SSJ2 Gohan had far beyond 0.1 picosecond reaction time. and if we keep going to Buu saga, time reaction will be greater. and just to remind you, that this is not the real time reaction, beause the real one is far far beyond this.
the likes of Superman, Superboy, Gladiator, Hyperion...etc have nanosecond reaction, it's clear now that DBZ fighters are very fast and can not just keep up with the likes of Superman but even surpass them in reaction speed.