delta400: "best" developer?

hi all.

i shot some rolls of delta400 120 in south west national parks during
my last trip there with my wife. i couldn't shot slower film for a
number of reasons, i'm sorry.

i'd love to be able to make some very large prints, up to 20x24"
--well, for me it's *very* large: i've never gone any larger than
8x10"-- and i'm trying to understand what's the best developer i can
use for my films.

i suppose i'll have no contrast problems because landscapes were quite
contrasty and i used some coloured filters to have even higher
contrast.

i usually develop my deltas in rodinal 1+50 --as from digitaltruth--,
but have in stock also some d76, tmax and xtol. i wouldn't want to use
anything else because i'm not very good in preparing my own chemicals
at home and i'm not able to find easily other developers here in
italy.

the idea is to get the thinnest grain possible to be able to enlarge
that much without getting baseball-sized grain for such subjects :)
--i like thick grain for jazz concerts, but this is different--.

any suggestion is appreciated.

regards,
--
Gianni Rondinini (30, tanti, RA)
VBR - Vero Birro Romagnolo
Hai capito, scelf?
.