I've never tried it but there was a dude on Pnet (largeish thread about his technique) that was getting some good results with extended development using HC110
I cant remember dilution but I believe he was using TriX possibly.
If I recall it wasn't a T grain film.
You could try searching over there and see what you think
I guess I can try to test some "stretched" HP5 or TX along with some Delta 3200.
As far as developer, what would anybody suggest beside Rodinal? Provided that grain is not an issue, it is actually desired.
if you want grain then give the Delta 3200 a good try, especially if you're pushing it hard. But read up on it and find the caveats about Ilford's incorrect development times. For 6400 develop to the 12800 time or get blank areas.
Delta 3200 is NOT Tmax 3200. It's very different. Still may not be what you want, but it certainly has a strong cult. Use it fresh. It spoils worse than slow speed film. Gets fogged from sitting around.
I use DD-X, but that keeps the grain in check. Of course it's still very apparent. But if it isn't enough for you then you might try good old D-76 or even Rodinal.