Ordinarily I'm right there with you - glaring errors put me right off. But if writing "Peters" for "Peter" makes you growl, we're not in the same league. (Especially given the somewhat casual approach to spelling and orthography in 17th c. England.) Things like that - mistakes that could easily have been made by a contemporary - just don't bother me.

What sends books flying from my fingers are characters behaving in ways that would be completely inappropriate, and paying no social price. Big problem for heroines in many historicals.