ahh the joys of suppension setup!!!! lol
Way I see it is that if your last setup was for 68Kg and now ur 78Kg then you'll want to harden the springs/shock as ur extra weight will cause it to travel more when it hits a bump. BUT saying that, it depends how and where you ride, and how you like the bike to move under you, like it to react to every bump, or to soak up even the biggest hole in the rd,
Personally I have mine set so that the front is a bit firmer than the back, but then I'm 14st with all gear on and I do like to have more weight over the front of the bike, I've got the back raised up 9mm using the thread on the back shock. front forks are at stock height.
best thing i can say is to adjust one thing at a time, ride it and see how it feels. there is no right or wrong answer. It's all down to personal choice!!