
This has been gone over many times of course.In general,I say no to keeping Cories and Goldies together for two reasons/
a) If your Goldies are bigger,they could possibly try eating one and have major probs in doing so,and b) alot of Meds do not sit well with Cories and therefore alot of times when people need to treat their tank,they're at a loss at what to do with the Cory's while they treat it.Even dosing tank with salt has to be done very carefully,because Catfish can be quite sensitive to salt.
c)if the tank's not big enough,the Cories also tend to hide-especially when the Goldies are bigger ones.
I have to be honest and say that I do have one tank that houses both.The Cories are actually older than the three Goldfish that are in there,but the Goldfish were given to me when they were 2-3 months old and still almost fry size.They've grown up with the Cories from the beginning,and have never once bothered them. I have to add that they eat all/most of my Cory eggs when they are laid,although somehow 3 babies managed to not get eaten.
The biggest Goldfish in that tank is well over 9 inches now.
I'm not saying it's not possible to keep these fish together,but I am saying to consider all options before doing so.