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Maybe I'm wrong here, but why would you ever take 2xST on a non-elite CC fex?
Let's just do the math real quick. The average roll on 1d6 is 3.5, so with a base statline of 2 attacks, the 2 x ST Fex gets 4 attacks per round. The ST/CC fex gets 4.5 on average. If you look at it this way, there is a 1/3 chance you will lose attacks with CC, 1/6th chance of it being the same as 2 x ST, and a 1/2 chance of gaining extra attacks. Basically 2/3rds of the time CC/ST is the same or better than 2 x ST. I like those odds.
I know a lot people will say 'I roll 1s' but the law of averages says that the CC fex will do more attacks over the course of one or more battles.
I think crushing claws are fun but only use them if you like them. I personally like them and think they're worth the extra 17 points. The random roll is fun and keeps people on edge which I find is a laugh. They look coll as well. On the bigger Carnifexes an extra 17 points isn't too bad. You can of course use crushing claws and a ranged weapon. Scything talons isn't that good when not used in pairs.
Assuming that we are talking about a Heavy fex, there is really no point limit besides whatever arbitrary limit you set yourself. This heavy fex would also have AG, etc...
So what do those 17 points buy you? Let's see:
Assuming you can get into CC for four rounds, that's two more un-saveable attacks on any MEQ you care to mention. At an average 15 point cost, even if only one hits, you've pretty much made back your point.
If you don't get into CC? Well, then this bad boy has been drawing fire like mad, letting your other gribblies and TMCs advance. Is that psychological advantage worth 17 points?
I dunno, CC looks like a good option on a 200+ pt melee monster fex.
The problem is, the more points you spend on a unit, the more it hurts when it dies. You need to try and strike a balnace between points spent and efectiveness.
Oh I understand completely, I'm not pretending that this is a free upgrade, but I see it making those 17 points back, on average, with the added benefit of your opponents being intimidated by it on the table.
I'm just thinking out loud here
I agree completely with the attitude that sometimes the most fun things to play are also not the most effective. Sometimes I throw raveners on the table just because I love how awesome the model is.