The camera move speed option at Options > Misc > Camera Move Speed provides a text input box. However, any attempts to replace an existing value there by a value of 20 by means of editing the text failed for me. Since these are fixed values, this should probably not be editable text in the first place, but just a drop down menu. Alternatively, and maybe better, allow a specific range of values without intervals (I assume there is any need for the steps of 5 in the first place).