I tried swapping stems about on my MTB and after buying two new stems finally got it perfect, but it wasn't a cheap process. If you're lbs won't let you try stems before you buy its probably worth trying to borrow a couple of friends stems to try different lengths/rises. Give it a reasonable trial though, it takes a while to get used to a stem. A shorter stem does slightly reduce leverage on climbing but did give very quick steering. Personally my back appreciates a short (75mm) 17 degree rise, but it wouldn't be a lot of peoples choice.

Richard