Agreed. I did a 7.5 hour ride in 2-3 degree weather on Wednesday with just a pair of Woolie Boolie socks on (no overshoes) and they kept my feet warm for it.
I had wollie boolies over a pair of condor merino socks. No overshoes though.
Overshoes have made the biggest difference out of everything I've tried so far, but for some reason it doesn't occur to me to wear them when I'm riding flat pedals.
DeFeet Woolie Boolie work really well for me.