Delta (Carry on)?

The most sensible answer come from the airlines.
You also are controlled by the class of service: First Class, Business class, and economy class.

There are no weight limits for carry on luggage, just size limitations.

No maximum weight applies to carry-on baggage except in the below stations:
•Singapore, Singapore - Changi International Airport (SIN) carry on should not exceed 15 lbs. (7kgs)
•South Korea - Incheon International Airport (ICN) carry on should not exceed 22 lbs. (10kgs)
•Beijing, China - Beijing Capital International Airport (PEK) carry on should not exceed 22 lbs. (10kgs)
•Shanghai, China - Pudong International Airport (PVG) carry on should not exceed 22lbs. (10kgs)