Wind resistance and weight is gonna slow you down much more so than 1.5" of wheel diameter ever could. Speed of 700c vs 26" has been argued and tested for years and will be from now on and proponents of either size will never concede or agree. There are go fast tires for 26" also just as there are off road tires for 700C It is just sometimes difficult to find either of them in a bike shop.

Many of us use 26" because it is cheaper and easier to make a very strong wheel in that size. Personally I use 26' since I tour on and off road usually on the same tour.
700C wheels can be built plenty strong, So it should not be a issue if you want 700C as opposed to 26" you just will pay more.