The only lighter tyre is an Avon CR500 but they're really designed for Caterhams and the like, not sure how they would fair on a heavier car with such a light carcass.
The 595RSR overall seems a good tyre from most reviews. The people who seem to complain are those who appear to be used to bigger budget semi-slick tyres and, in my opinion, have got used to how a tyre of that nature behaves and are perhaps expecting a tyre to do something it simply cannot.
For the money they're worth the punt and on a K11, which is fairly light, should be good as long as you can get the temperature in them.
