I think there's a misunderstanding there. There is some difference between 26" and 29er/700c tyres but the difference in rolling resistance between 23 and 35 would be negligible, compared to other factors.
My average speed on my Tricross with 32s and my Secteur on 25s is pretty much exactly the same. As @User says, narrower tyres are easier on flat surfaces but, sadly, I don't commute on flat surfaces.
I've just moved from 26x1.5 to 26x1.75 and the extra comfort is noticeable. Again, the tyres are heavier (not just from the extra rubber but 240 titanium studs might also have an effect

) but I can just ride through / over lumps, bumps and holes faster with the bigger tyres.
So, ultimately, you might be faster with narrower tyres if you ride on boards but the relative performance on "normal" riding surfaces would be down to the exact route you are riding as much as anything else.