RE: what skill level would you not recommend an Stype?
I had an s-type 115 when they first came out.
Its a very nice board and like you I'm 71kg and sail on a lake.
As Jonnyc said, I does feel small. I had hoped to use it as my main board but have now changed it for a Carve 122 which has given me a lot more planing and non planing time on the water. And when its windy I put in a smaller fin and still find it very quick.
I then got a 95l board for very windy days. Hope that helps.