I've done about 40 rolls of D400 in XTOL 1+1, shot at 400, developed for 9 minutes @ 70F/21C. Agitation, continuous first 30 seconds, one inversion thereafter. Works for me. I've also tried 1+2 dilution, two rolls of 35mm 36exp. in 500ml of developer, and it worked fine. The resulting neg looks sharper but a bit grainier than 1+1. I prefer the 1+1 look. At 1+3 it will apparently look even sharper and grainier, but you might need to expose at EI 200.(posted 8990 days ago)For suggested developing times for different films and dilutions, see Kodak's publication J-107, it's on the web too.
Hope this helps.