I really wouldn't downsize, because of the loss of comfort. Even 28's are still narrow tyres, and I only have one set of those, and that's only because the 32's I preferred almost rub the chainstays (on quite a sporty close-clearance Dawes 531 frame). A colleague has 25mm M+ on his commuting hack, purely because he got sick of punctures. I've since had a go on it and the tyres aren't my cup of tea at all. To take the weight those 25's have to be inflated rock hard with a track pump - even the front needs about 90psi. The resulting ride on crappy London tarmac isn't nice. Narrow M+ tyres are very unforgiving, as there is a lot of rubber in them in relation to the air volume. At least the wider ones have proportionally less rubber and more air so are a bit more supple.
I've never believed there was much, if any, rolling resistance benefit to running skinny tyres in real-world conditions out on the road (as opposed to a smooth track) Racers historically went for skinny tyres for weight minimalisation as much as anything.
Skinny tyres weigh less, irrespective of the type of surface being ridden on - so even if they don't give a racer any rolling resistance advantage, they will still be marginally faster overall because they have less tyre rubber to propel around, and less rotational inertia in the wheels.
