This coming from a guy with "chassis breaker" in his sig
I've used all sorts of brands of servos. Hitec is the cheapest. You get what you pay for. Their higher end titanium gear servos have done me good. I have sent in a few that had bad amps and pots. But I was running them in an 8ight-T, so it's a toss up as to whether it was the car or the servo. I have yet to blow any hitecs in my 8ight buggy. Their standard metal geared servos work well too, but the metal is a bit soft and the geartrain generally wears out before the electronics do.
Airtronics are generally good servos too. I had a 358 last a full month while improperly installed in my 8ight buggy (forgot spacers to keep it off the chassis)
Only owned a few KOs. They've always worked flawlessly; except in my touring car in which they seem to draw enough power to trip the BEC on the speedo (QC2).
Running a JR 9100T in my crawler with no problems, but I haven't had it that long so I can't comment on longevity. But the whole reason I bought it was because I heard good things about 'em.
Haven't run Futabas since I had a JRXT, but they have an excellent reputation too. But they are more expensive.
Oh... to answer your other question... there is such a thing as overkill, but it's better to have too much torque than too little; unless you don't have your EPAs set properly
If you have your heart set on those KOs, then by all means, get 'em.