My own experience with Moultons and Bromptons (16" wheels, so much greater difference than 700C versus 26 inch) suggests that, for similar rims and tyres, the difference between 700C and 26 inch would be negligeable.
I have done 180 km day rides with old F-frame 16" wheel Moultons and Bromptons. Significantly less tiring on the Moultons compared to Bromptons, probably due to effective suspension. At that time I didn't use a 26" wheel bike for long rides (in 26 inch I only had a mountain bike with off-road tyres), but did have a lightweight touring bike with 700C wheels.
Comparing my 700C bike with my Moultons, the latter were better for comfort over long differences, but marginally slower, perhaps due to a combination of heavier weight and less suitable gearing.
This is on road. Off-road or on bad road surfaces a big wheel with a fat tyre works much better than a 16" wheel. But the difference between 26" and 700C is only about 11% at the rim.
In practice, 26" wheels are generally heavier to fit wider tyres (also heavier) so a 700C bike with thin lightweight tyres should perform better than a 26" with heavy tyres. But I find that a 26" wheel bike with lightweight but fat tyres (Supreme 2.0 in my case) rolls very easily, and, though slower, is more comfortable on long rides than my 700C x 28mm bike. So despite the weight difference I tend to ride my rather heavy 26" wheel bikes further than my 700C bike.