30: As I recall, without the C17/C18 exchange, joseki is the pincer at C11. Indeed, either pincer works well with your strength in the lower left, but C11 has the additional advantage that in some lines you can slip under with C13.
There is also tewari analysis which gives you a suggestion of C11. As you probably know, in the mixed three space extension, there are three recommended invasion points, 'a', 'b', and 'c' in this diagram:
$$B
$$ . . . . . . . . . . .
$$ . . . . . . . . . . .
$$ . . . . a d c O . . .
$$ . . . O . b . . . . .
$$ . . . . . . . . . . .
$$ . . . . . . . . . . .
$$----------------------
- Click Here To Show Diagram Code
[go]$$B
$$ . . . . . . . . . . .
$$ . . . . . . . . . . .
$$ . . . . a d c O . . .
$$ . . . O . b . . . . .
$$ . . . . . . . . . . .
$$ . . . . . . . . . . .
$$----------------------[/go]
...but the high middle invasion at 'd' is usually considered ineffective, because the defender can play like this:
$$B
$$ . . . . . . . . . . .
$$ . . . . . . . . . . .
$$ . . . . 8 1 4 O . . .
$$ . . . O 5 2 3 . . . .
$$ . . . . 7 6 . . . . .
$$ . . . . . . . . . . .
$$----------------------
- Click Here To Show Diagram Code
[go]$$B
$$ . . . . . . . . . . .
$$ . . . . . . . . . . .
$$ . . . . 8 1 4 O . . .
$$ . . . O 5 2 3 . . . .
$$ . . . . 7 6 . . . . .
$$ . . . . . . . . . . .
$$----------------------[/go]
...or different sequences which lead to similar patterns with the same result: the defender stays connected and the harder the invader tries, the more stones he loses.
If you transfer that logic to move 30 in your game, it looks like this:
$$B
$$ | ------------
$$ | . . . . . . .
$$ | . . . . . . .
$$ | . . . X . . .
$$ | . . . . . . .
$$ | . . . O . . .
$$ | . . . . . . .
$$ | . . f X . . .
$$ | . . . . . . .
$$ | . . O . . . .
$$ | . . . . . . .
$$ | . . . . . . .
$$ | . . . . . . .
$$ | . . . . . . .
- Click Here To Show Diagram Code
[go]$$B
$$ | ------------
$$ | . . . . . . .
$$ | . . . . . . .
$$ | . . . X . . .
$$ | . . . . . . .
$$ | . . . O . . .
$$ | . . . . . . .
$$ | . . f X . . .
$$ | . . . . . . .
$$ | . . O . . . .
$$ | . . . . . . .
$$ | . . . . . . .
$$ | . . . . . . .
$$ | . . . . . . .[/go]
The sequence is different, but the potential is the same: you are threatening to play at 'f'. ( Black's 3-4 stone does complicate matters for both sides, so the reading may get tricky, but the idea still holds )