I've come to the conclusion that targeting mash pH much below 5.4 for most ale styles tends to be too tart for me. Of course, most ale yeast produce a beer pH that is lower than that of a lager yeast. So that probably biases my findings. With that difference in typical final beer pH for those yeasts, it does seem that it can be more appropriate to target a pH less than 5.4 in pursuit of 'crispness'. Unfortunately, I brew far more ales than lagers and can't develop much experience in the lager field. I will bow to the findings of active lagers brewers with respect to mash pH recommendations.