What is (are) the longest cage derailers made? I have a Shimano Acera X and it is as long as I have seen. I want to drive a Suntour 38 and was told a Suntour AG derailer will work but have not come across one of those yet. Some SCRAMs are very long. I will be using (or try to use) a 20 in the front (also Suntour).

A Shimano Altus front derailer seems to be able to handle anything because it goes down to the chain tube.
thanks