This has been discussed many times before and I think the consensus is that the reciprocity chart produced by Ilford is of little value with the Delta films....

I have said it before - Ilford are missing a trick because low level light shooters, astronomers, anyone using film for long exposure purposes is likely to consider Acros first as they boast about it's excellent reciprocity characteristics.

Delta is probably just as good - It is just that far few people seem to know this