The 7.9 will definitely surf well off the wind and I suspect you can get them to plane up wind under the right conditions. I have an S2 9.1 which has a fixed keel and if I do not have too much weight on the boat, say only three crew it will pick up and plane on a close reach, really fun when it does that.
It will easily surf for several minutes off the wind even in flat water, although it takes winds in the mid twenties to do that. The 7.9 has a similar hull shape so it should as well. There is a 7.9 locally here that is for sale. I will try to find the details and PM you. Has a trailer so easy to get home.