I do urge you to get Blue Remembered Hills - I picked it up in the university library in Ayr, thinking it was Dennis Potter's play, which I fancied rereading since I'd acted in it (I was Donald because of a man-shortage) - and had to be hauled away. It's most odd, though.
I do know what you mean about People-from-the-Past-speak, though I think historical novel dialogue presents almost insurmountable challenges. I flinch from ay-me-zounds-I-pray-thee-not-Lucrezia but also from anachronism - the unconsidered "lovelys" and "sures" that pepper a lot of historical fiction (in my early schooldays "OK" was still considered a vile Americanism tolerated in the playground but quite unsuited to classroom use -- and this was an ordinary village school) make me rage and grind my teeth. The middle ground does seem to be something like what Sutcliff comes up with, but the disadvantage of it is that it's just a signal that we are now in the Past (the cinematic equivalent is that clasp-forearm-hearty-laugh thing that, if Hollywood is to be believed, was the preferred greeting of adult males between the epochs of Homer and Henry Fielding - what happened to "Good morning", I wonder?) and it can't really accommodate class difference without becoming hopelessly messy.