I would like to take my three 20 kg suitcases to Hong Kong.

Do you recommend paying the extra fee in the airplane or is shipping two of them via China Post cheaper?

Thanks!

check if you chinapost you may hit customs issues. sometimes you can prepay for extra luggage on flights and it is cheaper than excess baggage on check in. or you could take high speed bullet train from kunming to shenzhen takes 8 hours and then on to hk.

Thanks for your advice Dazzer!

Are there no luggage limitations for the train?

Do I need to book tickets ahead on trip.com?
How much do I need to estimate for the travel from SZ to HK?

Guangzhou Hk is about two hours as I recall. C-Trip it.

From SZ to HK Central is about 35 minutes on the commuter train after you walk over the border & thru Immigration. SZ borders on HK territory.