I'd feel a lot more comfortable shipping them than flying with them. Get the hard cases regardless, especially if you have the chance to borrow or rent them. Plus, you don't have to schlep the cases through the airport along with the rest of your luggage, which is a MAJOR plus. If you're staying in a hotel, let the front desk know to expect the boxes - they do that all the time, often with photography and video gear, or salespeoples' samples, that are worth at least that much. Insure them through the shipper just like any other parcel - outside of shipping, your homeowners'/renters' may cover them, but definitely check - often they require a rider for sporting equipment over a certain value, and you'll want replacement value anyway.

I ship mine in a Thule case twice a year, sometimes more. Coming up on the sixth time, no problems yet [touch wood]. Use plenty of pipe insulation on the frame and foam or bubble wrap on other stuff, swipe some drop-out spacers from your LBS, take the RDs off even if the case instructions don't require it, and cinch everything down tight.