Stuart & co,
This is my late entry:
John Lawfull Son to John Slorach & Jean Siveright in Glen
garrack was born the 12th & baptized this day witnesses John
Sandieson younger in New Mill Johns Wright Wilson & Steinson
Jean Stitchels Janet Milles
Initially I thought it was Stimson (also a version of Stevenson), but I have to agree with Forfarian that it looks more like Steinson, even though the n doesn't match others in the extract; it looks like the writer wasn't sure how to spell it or was worried about going off the edge of the page, so stalled in the middle of the word.
Stitchels (or Stitchils): all I'm confident about are the S, h, l and s. The first vowel seems more like his i than e, but what I reckon to be the second vowel is ambiguous. The other tall letters look slightly more like his uncrossed t than his looped and less vertical l. There is a place called Stichill, near Kelso in Roxburghshire, so that may explain its origin.
I'm pretty sure that's an s on the end of Mille. More importantly, there's an s on the end of John, to save him writing it 3 times: ie Wright, Wilson & Steinson were all called John, which explains the &. (The Scots at this time also have a tendency to put an s on a surname when there are 2 or more the same.) That means there are 4 Johns, not including the father and child; I recently saw a page of Scottish baptisms where almost every witness had the same forename as the corresponding child, so I suggest these Johns were probably all godfathers after whom the child was named, rather than necessarily relatives.
The Oxford Dictionary of English Surnames gives the alternatives Sievwright, Sivewright, Seivwright and Sevewright, but if you're using the Soundex on SP all of these and more should come up anyway. But you've probably done every possible SP search you can think of, so at least you might have an idea whether the families were established in the Keith area. Unfortunately the excellent Lands and People of Moray series of books doesn't seem to have stretched to Banffshire parishes, but the Moray archives in Elgin (their details are on the Moray Council website) will know what documents there are beyond OPR, so well worth contacting them for advice.
These are just my opinions so feel free to criticise, but I hope at least some of the ramble is helpful.
James