A higher reading rate, with no loss of comprehension, will help you in other subjects as well as in English ,and the general principles apply to any language .Naturally, you will not read every book at the same speed. You would expect to read a newspaper, for example ,much more rapidly than a physics or economics textbook –but you can raise your average reading speed over the whole range of materials you wish to cover so that the percentage gained will be the same whatever kind of reading you are concerned with .