I have found that DD-X actually keeps quite well, as long as you make sure of sealing the bottle tightly, for instance with a thin piece of plastic screwed in between the lid. You are right about DD-X's quality, it is a lovely developer. Unfortunately I cannot buy it in Holland and I have to order it in the UK. This is fine when I am in Scotland, in my friend's darkroom, but if I am at home it costs me an arm and a leg to have chemicals shipped to Holland.
Thanks anyway for your comments. I think I will give the Delta 3200 a try.
p.s. does anybody happen to know whether Fuji Neopan 1600 comes in rollfilm?