If you are worried about stiffness, Ambrosio used to make a rim called the Thesis that had a slight V profile. You might be able to find them. I see on ebay.co.uk and ebay.de periodically. You should also consider the Nemesis, but it is not as light as the Crono F20. If these are purely for racing, I think the Crono F20 or an older Mavic rim (Gel330) would be my choice.