high cond is viable, in fact i would say it increases you chance of winning, but increased IPs are an issue. outside of heavies i would never use more than 22 cnd, but normally i don't use more than 18.
the trick is to use your high cond by using more agg and pow, and make your opponent follow you where he will get fatigued. 6/6/8, 7/5/8, 8/4/8 and 8/5/7 are good tactics for high cond fighters. probably not in round 1, but definitely round 5 onwards. starting fights with 6B/6/8 is a very good way for a high cond fighters to start against his opponents. the opponent will have difficulties winning rounds without getting fatigued while you stay relatively efficient and with no fatigue.
high conds most effective ability is the rest between rounds. more cond, means more lost endurance which means more endurance gained between rounds. you will get to the point where you can no longer get anymore tired as the endurance damage dealt = endurance gained by rest.
in short, win as many early rounds as you can without using agg high enough to get any fatigue. sit at your fatigue threshold as he tries to win rounds and gets badly fatigued. since the opp spends most of the fight trying to win back rounds, you take less damage. for high cond to be viable, you have to use it.
the big problem is 2 KP is usually hidden. people cant scout it and therefore dont expect it so people dont fear it. 18/6 KP is easily visible and certainly changes the way an opponent fights. opponents will use higher DEF and the KP guy takes fewer IPs. if you have 2 KP, people will go as hard as they normally do and unless you have enough KP to KO them (2 is not enough usually) then what have you gained?
if there is a prevalance of KP fighters, your efficiency doesn't mean near as much and most people will assume you have 0 KP. having 2 KP here is useful because KP fighters will go harder than they should and can KO themselves.
i would never drop chin for KP, i would more likely increase chin so i could use my KP more effectively. using KP to get late round stuns for an endurance type fighters could work.