Hi Tom,
Can I ask what telescope you are using? Magnification alone isn't a good gauge to help you with. The size of your scope is a better indicator. If your scope is 4" in size, you'll struggle to see much with M20 other than a roundish smudge. A 10" scope and a dark sky with good conditions and you'll never forget your first look of M20 - I never have!
M20 is one of the objects I've got penned in for a sketch this year. Here's hoping.
In the mean time here's a link to
a sketch of M20 using an 8" scope by Janis Romer, though it doesn't note what magnification was used.
Mental.