37/6s are 90mph capable as are the 37/0s. They are also fitted with cast bogies ex class 50/55. A lot of network rail test trains require 90mph running and blue star coupling, DRS have a small fleet of 37/0s for this. The main problem with the 37/6s is wheelsets. 37606 was tyre turned, but aquired wheel flats soon after and the wheels were already at scrapping size so it was game over.