This comes from my notes from Yogi Breisner’s lecture at the BE Training day at Newmarket in 2010.
His thoughts on bitting, especially for the XC phase:
Leverage bits affect steering.
Then, to steer, there is a vice action on the poll downwards, from the martingale’s pull.
Then the horse runs from the bit, stiffens up.
Horse is more likely to slip over.
There are lots of SJs down on the final day of a 3-day because of XC bitting – horse is sore in the mouth, worried about the mouth.”
Sorry, I realise the notes are a bit staccato but I think there are some real gems in here, worth mulling over when considering whether to go for stronger bits, especially leverage bits, or not.