BB - I always take games seriously. But in the sense that I can learn a lot from them.
If there is indeed only one card that can beat you, you must have a Wizard and you are worried about the last Wizard.
I wouldn't worry about rkoelsch. He's made it very clear that he doesn't think he can make his bid.
As far as taking the Ace of Clubs away from CT - yes you should have. For two reasons. First, there are 3 extra tricks bid this round. That means that in general, the hands are fairly strong. If you indeed have a Wizard, then it wasn't as crutial, but still, waiting too long could potentially get your Wizard stolen.
The second reason, and if you do have a Wizard, then the odds of making your bid was good, so this is the more important reason, CT had 160 points before this hand. I had 50, and rkoelsch had 110. You had some level of control over who you "messed up". The longer you wait, the less control you have. It is still reasonably early in the game, so you may consider certain players to be bigger threats in general, but all else being equal, it always pays to try to hit the person in the lead.
I suspect, however, that it doesn't really matter in this case unless I am mistaken about which card CT has left.
But don't worry. Even though I take games very seriously, I do realize that they are only games. I intend to be a good sport about everything, win or lose