Hi I'm in need of new running trainers. I suffer from slight lower back pain now and again and as such have trailed a number of pairs over the years. By far the most comfortable ones for me are asics gt2170's but the new design for this year is called the 2000. I'm just wondering if anyone has had both these pairs and can tell me if there's any big difference? I'm hoping the fit is the same but also hope there's been no major revision as I don't want to take gamble with my back again.