Actually, running the 650c/26" is Deb W's idea, and how her bike was built. Her bike sounds a lot like the one Susan wants, so perhaps they should chat a bit.

The builder that installed S/S couplers on my touring bike strongly recommended 650c/26" for travel bikes, since the airline case limit is 26". You can fit a 700c wheel, but have to put it in at an angle and/or remove the tires to fit it, a real pain when packing and unpacking. Susan, you will notice that it is a bit more work to pack/un pack an S/S coupled bike than a friday, but well worth it in my opinion for the improved ride quality. Just discuss all these issues with your builder, that's the whole point of going custom, to get really knowledgable input. We can only guess what the differences are between the 2 designs in terms of handling, TCO, etc., but obviously your builder can discuss with you better your specific designs.

I will be honest though, not sure a 26" wheelset is necessary, since the terry tellus 28c tire is fine for most touring applications, but its clearly a good option for versatility which I think you want in a travel bike.