Personally I don't think it's sensible to use one to judge the other like that. Hydromorphone and codeine are metabolised to different chemicals by, as far as I know, different enzymes. There are substantial individual differences in the amount of these enzymes in our bodies so the apparent lack of effects from the hydromorphone is not a perfect indicator that you can then go on to take massive doses of codeine without risk. In fact, if it was the other way round and you were not an effective metaboliser of codeine (not an uncommon genetic trait), you could easily justify taking a massive overdose of a stronger opioid - one which you can metabolise effectively - and unknowingly end up in a lot of trouble.
Anyway, since codeine's weak as hell, there's probably far less of a problem. I wouldn't personally drop a 500mg CWE first time for various reasons. At least do a trial run @ ~300mg and, as Morphling suggested, keep some antihistamines handy because you might not be able to stand the itching at that dose. 300mg would still be enough to knock you sideways if you're completely opiate naive and metabolise codeine better than you metabolise hydromorphone. At any rate, a lot of people will tell you that any dose over about ~450mg is a waste of time because of the dosage ceiling; although I've never personally hit that.
