I don't really know if a 5% boost is enough for the average fast ones to catch you. I just guessed and moved on, so might need another 5% or 10%. You will find out.
Did a bit of testing on Insane/Nightmare run.
10 block gap, straight flat tarmac road, I fired a shot and ran the other way:
Faster than player (fastest to slowest),
biker rad - is pure evil, he caught me @89 stamina
biker - caught me @75 stamina
dog - caught @65 stamina
direwolf - caught @50
cheerleader rad - caught @50
business man feral - caught @40
cheeleader - caught @30
stripper feral - caught @30
darlene feral - caught @30, faster than darlene rad?
old timer feral - @10
About same speed as player, I could run down my stamina to zero:
arlene - she's slightly slower
arlene feral - caught up right behind but didn't trigger attack
arlene rad
business man
burnt
darlene
darlene rad - caught up right behind but didn't trigger attack
nurse
nurse feral
snow - he's slightly slower
snow feral
stripper
wight rad
Slower than player:
farmer
football player
utility worker
military rad
old timer
bear, wolf, mtn lion - gave up chase in seconds
I could out run everything even radiated biker on uneven hilly ground, any uphill or downhill slowed them down and I could get away.
Personally I'd like them a tad faster so the faster ones really give me the sh**s, I think zombie speeds really change the game, stepping out becomes strategic instead of a free for all looting/questing session, anyway hope that helps.