I was one of the "slow" pilots last season, i only got to race in 2 or 3 races. So i never had to carry extra weight. But, i think you guys should max the total weight to 50 kg . Using ballast is fair till some point. 70 kg is maybe a bit over the top.
Whatever you guys decide to do, it will be fine. In my opinion, ITCC was the best event in 2009, and im sure it will be in 2010, even with 70 kg.