From the little bit I have used TMAX RS developer, I was generally pleased. I used it at 75 degrees, which is the temp I had heard it functions best. I don't recall much beyond a generally favorable reaction; it did yield nice tonality for the few sheets of TMX I developed in it. I tried it because the developer I was using didn't fare to well with rotary processing (catechol based, tanning type), but once I had solved the problem, I went back to my standard brew. I do recall thinking that I could probably get to like TMAX RS, though.(posted 8430 days ago)I have never used it with Delta 400, although I would expect they'd mate pretty well. Delta 400 seems to look nice in every developer.
Incidentally, if you are doing sheet film, do not use TMAX developer; you must use the TMAX RS version. Regular TMAX developer is prone to diachrotic fog with sheet film.
You can find some worthwhile information from John Sexton on using TMAX developer with TMAX films at this site: www.cs.berkeley.edu/~qtluong/photography/lf/articles/sexton-tmax.html