The real value in a compression test is that the values are close for each
cylinder. A leakdown test is of course much more accurate but a compression test
is so simple and fast that it can give you a lot of info in a short time. I
usually don't worry about low readings as long as they all match. Neither one of
your examples would worry me at all. The 170 across the board or the 205's with
one 200. I would use the compression check as a first test for issues and if you
need more accurate info move on to the leakdown test.
hope this helps,
Craig
the Gorge VW club