I was just able to use 26 Delta gift cards in a single transaction (mostly $50). It did take close to 2 hours to process.

From what the agent said, anything over 3 gift cards requires a supervisor. The process involved me reading all 26 gift cards, which took maybe 20 minutes (including setting up the actual flights and her verifying the process with supervisors). Somewhere between 3 and 26 gift cards they started running into system issues (which explains the other hour and 40 minutes). Everyone on the Delta side was surprised it took as long as it did, but they had never done that many before either. They didn't tell me what they were doing to process, but I did get an email while I was waiting on hold, that I had a travel voucher that was worth my first 17 gift cards.

I have no status and did this by calling into the main reservation line, so this is available to anyone who's got some free time.