A Fanfic Foray and an Historical Query

It's been quite some time since I ventured into the realm of fanfic with my writing. There are a number of reasons for that, the most prominent of which is time. I'm simply too busy playing with my own toys in my own universes to be bothered to play with someone else's in theirs. Lately (like, yesterday), though, I made an exception. Funny thing is it's not a fandom in which I'm active, although I do enjoy permutations of it.

Okay. From the top:
A friend wrote an m/m ACD-canon fic for Holmestice over on LiveJournal (I'd tell you which one, but the authors haven't been revealed yet.), which I beta'd for her, and then she asked me to write a smutty follow-up for it. Now, m/m smut I'm cool with (obviously), but Victorian m/m smut? In the voice of John H. Watson M.D.? Yeeeeeah. That was a writing challenge. And I'm still not sure I met it. She said her brain had to unbend before she could get all technical on the fic. (Side note: I bent her brain in under 1400 words. I'm so pleased. ;-> )

All this got me thinking about different periods of historical fiction. "Historicals" are sort of lumped together in my head, but Victorian is completely different from Regency, is completely different from Elizabethan or Jacobean, from Restoration, from pre-WWI, from mid-20th-century, from, from, from... Each has its own distinct voice, and mastering even one can be a challenge, never mind mastering a variety. And then there's the question of historical accuracy--how much of it you need for your story to carry plausibility vs. how much your readers can take in and still feel the necessary emotional connection to the characters. For example, I started reading a book lately that was built on an historical inaccuracy and an anachronism. It's clear that others love this book; I picked it up at the library because it was a "top pick" in the local newspaper. I quit reading within two chapters because the blatant impossibilities over-powered any feeling I might have had for the characters.

So, this question goes out to the writers and readers of historical m/m (or other) romance: How important is the "voice" of the period compared to the accessibility of the characters and the story being told?