US highway traffic tends to run about 70-75mph (110-120kph) regardless of the posted speed. I like to drive 5-10mph faster - the US DOT statistics say that's actually the safest relative speed. Any faster than that, and I find that it pisses off the people you want to pass anyway (people think you're going too fast and want to play junior policeman). So, 80mph or 130kph for me.
70kph? I hope you don't mean on the highway - you'd be the single most dangerous thing on the road around here.
This is from a study done in the 1960's, showing collision data as compared to relative speed. As you can see, about 7mph over the prevailing traffic speed is the sweet spot, slightly less at night...
Other studies have shown a higher relative speed being the safest (Google for Cirillo relative risk curve).
Being a mobile chicane is not smart.
The problem with these studies is that they omit single-car accidents which obviously skew the results somewhat. Still, I find that driving slightly faster than the prevailing speed better allows me to mentally keep track of where the traffic is, and I'm not splitting my attention with the rear-view mirror nearly as much.
I guess the other problem is that the strategy only works if it's a fairly well guarded secret. Everyone can't drive 5mph faster than the average.
In town is different, since the main danger isn't the cars traveling with you, but things like cross traffic, pedestrians and bikes, etc.; i.e., things you need to see and have time to react to. So slower is better, within reason.