The 105/1.4 is no replacement for the old veteran f/2.5 as they can co-exist happily. My experience for what it is worth.
The f/1.4 does much better than the f/2.5 if combined with extension. However, as it is 'E', one either needs the indefinite patience to manipulate the aperture to a desirable setting, or aim for an extension tube with pass-through contacts. In the latter case, don't forget the inner opening need to be as large as possible in order not to cut off peripheral rays. Erik made such a ring for me from a junked TC-14E.2 (thanks again for the birthday gift!!).