I've given up with overshoes for the most part and i've now added Waterproof socks to my armoury. Aldi had some for £14.99 last week. Sealskinz etc. I've had every brand of overshoe from BBB to Sealskinz. I've even added a carrier bag around my feet as an attempt to improve the situation. Water invariably gets in through the cleats, or drips down the leg into the foot. And if you go through one of those lake like puddles then you're in for a treat. I've now had two weeks of dry feet in adverse weather.
My aging overshoes which were excellent but no longer made have finally given up the ghost. I bought some DHB Neoprene ones and they have worked well so far. All overshoes will let some water in through cleat area but at least wit the neoprene even if wet feet stay warm
I came to this thread hoping for some revelation on how to keep feet dry; instead i find the same gripes i have.
I commute 5 days a week and have just started wearing my DeFeet overshoes (as well as DeFeet Woolie Boolie socks) to keep warm. They're decent for keeping tootsies warm but in no way waterproof. They fray easily and with constant use will start to split and separate within a few months. I tend to sew them back up but it's a pisser and, honestly, i wish i didn't have to do it simply to keep the warmth around my feet.
I cannot recommend BBB overshoes for constant commuting at all. I have had three pairs of the HeavyDuty ones in 5 years and they fall apart at the seams as soon as you look at them. I have spent many many nights sewing them back together. It got to a point where i was transplanting older pieces of the neoprene shoes to the new ones to patch up holes and where the seams had come apart. That said, they are relatively decent at keeping the wet out when they're sealed. YMMV, and bear in mind i am a thrifty bar-steward when it comes to kit.
A pair of DHB neoprene toe covers for insulation with a pair of Funkier overshoes on top for wind and rain protection. Water will get in eventually so I wear a good pair of merino socks that will hold onto the water and allow it to eventually warm up.
I experimented with chemical foot warmers last winter in icy conditions rather than wet. They claimed to keep feet warm for up to five hours. Didn't really notice any difference until they stopped working after two hours then my feet got really cold.