The countdown was certainly long and slow enough to give her plenty of time to stop things - proof to me that Sherlock did not want to kill himself...

Sorry for not making this clear. It was a reaction to bb saying:

Just a couple of gut reactions:
1.  I think Sherlock accepts that his death may be a consequence of his work, but I don't generally think he is suicidal.

To me, the pill scene is more than accepting death as a consequence of Sherlock's work. There is no need for him to take the pill. The cabbie has been found guilty. He has no real gun. So there is no actual need to go further and yet he does. 

Taking a potentially poisenous pill just to prove one is right is for me a sign of not valueing one's life at the very minimum. It could also be a sign of a positive death wish. Or complete idiocy... I dare say SusiGo's point of view is the most charitable one.

Yes, I think there's maybe a bit of both.  This sort of murder was designed to lure him in and fascinate him, and he was intrigued by the puzzle and wanted to win. He had to know that he was right and prove it.   It's almost like his slip-up with Norbury.  But I agree, there is also a bit of not valuing his own life, and putting himself in the way of danger. 

I kind of like the arrogant side of him, so I maybe lean more to that in my interpretation.