It highly depends on:
1) Cabal/Role. Scribe warrior is not going to have the same PK score as a scion warrior, assuming they both are equal in all other areas (played the same player, for example). They have different set of enemies and different guidelines in PK.
2) Eq. One may be lucky to obtain some good pieces and other will be not if, for example, strange bracers (defiance/insert-your-item) is hoared.
3) Current set of enemies. Even if we have two chars in the same cabal at different times they may experience completely different opposition. For one it may consist mostly with newbies and other may face skilled permas.
4) Style: defensive/offensive.
5) Fairness (no multikilling newbies, no cheap kills).
6) "Smart" logins. In order to maximize kills per hours ratio people login against easy targets and logouts agains tough permas. I observe this behaviour quite often.
7) Current balance. For example, when hurl throat became 3 ticks silence we had some successful dagger specs and when it changed back to 1, we see less so. Similar things happened to many other classes (often after revamps) and I don't even tell anything about poison thieves at some point.

So, in conclusion, there is no easy measure. And certainly raw PK score is not one.
It is just feeling that many veterans may have, something like:
"This char does amusing things and often provides challenge, respect" (even if he dies often and his PK ratio isn't shining).
"This one is a harvester for cheap kills, burn"