Reason I asked here is that I did a bit of testing but the results are inconclusive to say the least.
I rolled up a character with will 4 to start, and increased psychokinesis to just 40 (so I could take premeditation). On this guy, telekinetic punch and electrokinesis both worked quite reliably all the way to the end of Junkyard, and into the warehouse and rail crossing sections.
I then tried a will 3, psychokinesis 0 guy. He couldn't even land the stun against rathounds.
A will 3, psychokinesis 15 guy could comfortably land stun against the initial rathounds, and the fight with the woman with 2 pet rathounds. I didn't take this build further at this stage, as I thought I'd ask here in case someone's already done the investigation or the mechanics have been detailed already. I'll probably run this build with the psychokinesis kept at 15 to see when it starts to feel unreliable.
So at the moment, I'm really not sure if this is a threshold thing (i.e. there is a hard minimum that you need for the stun to take effect, but then raising your skill higher doesn't make it more effective) or if it scales linearly with increasing skill but is subject to a hard cap.
I'd certainly have expected the will 4 / pscyhokinesis 40 guy's effectiveness to be very low by the end of junkyard for example, but it was still quite reliable at that stage - certainly it didn't feel qualitatively worse than my maxed out psi guy.
Also, nothing in the description of resolve suggests that its a contested roll (vs attacker's skill) - this doesn't mean to say that it isn't contested of course, but I could easily see it being a straight attribute check for the defender independent of the attacker's skill.