The only rule about preempts is "Don't make a preempt your partner won't expect". Have an agreement with your partner, and stick to it. What that agreement is is (almost) irrelevant; it is certainly less damaging to your results than violating the agreement.
I play duplicate, and mostly matchpoints. So read this with that slant. Although I will note that even at IMPs, very aggressive preempts are common even at the top levels, because they work.
At rubber, remember the golden rule of preempts: You are deliberately paying to extend the rubber. If you're playing with the weakest player at the table, the job is to get out as cheaply as possible and cut someone better, not pay a premium to continue longer. S.J. Simon's Why You Lose At Bridge is just as right about that as it was in 1946 when he wrote it.
End of digression.
If your agreement is "Rule of 2/3" then with 3 tricks opposite a vulnerable 3H bid, bid game and expect to make it. Great! You'll score a lot of -140s into -100 or -620s into -170 when you pass, but that's the choice you and your partner have made.
If your agreement is "7 cards, hopefully to an honour or two, and no more than half a defensive trick outside", then more power to you! You'll get a lot of +170s that the room bids game on, and the odd -500 into nothing, but the opponents are figuring out what to do at the 3 level when the room gets to open 1 a lot more, and they will not bid as well on average - and -100 for 3D-1 scores really well when other tables' opponents know to matchpoint double after the competitive auction, or get to wrap up 110 in 2S.
In particular, 3C (and 3D in systems with a conventional 2D call) are frequently very aggressive. They're "only as preemptive" as 2S, so these pairs treat them the same as 2S (even though, if doubled, it's down one more). If it works for you, go for it! If it doesn't, don't! (see below for my almost reverse of this decision).
I play very sound preempts with one partner, because she's one of the best card players in the city, and expects to win by taking one more trick than the field on the play and on defence (frequently doubled).
My agreement with my other regular partner is "3C or 3D opposite an unpassed hand will not feel guilty putting down dummy in 3NT. 3H or 3S, especially NV, is anything goes." (within the context of "anything goes" 2-bids and NAMYATS 4-major)
I've even played a system where your example of CAQJxxx is too strong for a 3C bid.
One thing my teacher said, 30 years ago, was "think about playing 5/8/11." That is, when you're vul and they're not, your preempt will go down 2 tricks (500) opposite a bust; at equal vul, 800 (-3V or -4 NV); at favourable, -5 (1100). Note that this style is basically trying to disrupt opponents' slam bidding, not game bidding. Again, if that's your style, go for it!
If I have to play with a new partner at the last minute (which as a club TD I am frequently called on to do), I ask 4 questions, and hope to muddle through the rest. One of them is "what's your preempt style?" It's that important to be on the same page.
I'll end with a link to a discussion on another site about preempts. Note especially the thread at the bottom, from a English International player (my emphasis):
was opened 3D, first seat, favourable vulnerability at 4 of the 5 tables in the English trials. The fifth opened it 4D.