Looking back, Garmin recorded temperatures between 7 and 9 degrees. But it did feel much much colder. No wind chill to speak of (besides your own speed of course) but the humidity probably played a big role in this.
Your skin is basically one large heat exchanger. Wind on the skin increases the rate of evaporative cooling, which takes energy, known as windchill, as the boundary layer of air against the skin gets replaced more frequently . This is why a windproof works so well at keeping you warmer, as it slows that form of energy loss, by helping create a still layer iof air against the skin.
Water is a a great conductor of heat. So if you have it on the skin either sweat or rain, you have another source of heat loss. So that's what your base layers job is, to wick the water away from the skin, so it can move out into the other layers escape.
Main job of the rest of the layers is to trap air. Air is a fantastic insulator, provided it not getting replaced all the time (see windchill). This is why Down in a windproof shell is so great as it traps so much air around the body.
Modern waterproof shells struggle with aerobic exercise like bike riding. So often the sweat that is trying to escape condenses on the cold outer shell, then soaks back through the layers over time. The water displaces air, and eventually soaks back to the skin. Insulation value of the layers plummets and the skin cools from conduction heat loss as weel.
Materials like Primaloft works in the wet by maintaining loft and retaining the ability to trap air. It is the same with hydrophobic down (down treated to repel water).
So staying warm in wet and windy conditions is tough. Getting water away from the skin, then out through the layers, wind proofing to trap layers of air (and slow water ingress) are key. A windproof can work better than a waterproif shell if you are working hard aerobically, aka hills or headwinds. If you are working only moderately hard than a traditional shell may work better.
I last wore a waterproof shell on the bike during LEL 13. Since then I have worn a wibdproof as my outer in all weathers. But having had a cold wet Easter Arrow I have just bought a new Paramo Jacket. I had one in the 90's and really rated it, but found it too warm. Fast forward 25 years and they have lighter versions for aerobic activity, and pit zips you can adjust on the move to regulate temperature to stop overheating (and thus sweat which will cool you later).
Always worth reviewing your set up after a cold wet ride to see if it still works for you, under what conditions it fails to work, and if so why. Then look at what replacement layer(s) may work in those conditions.
Last thought I will leave you with is Vapour Barrier Clothing. It turns layers on its head and is generally used in very cold environments (-25C and bellow type cold) to stay warm in very thin clothing. Have a read here
https://sectionhiker.com/vapor_barrier_clothing/ but basically if you are chilled putting your waterproof against the skin, and the other layers outside may, counter intuitively, be warmer. It worked with neoprene waterproofs and with PU waterproofs in the 80's in winter. Plastic bags next to skin on feet or hands is also a good example. You want the bag under the sock / glove, not over.
A younger life spent climbing mountains in the Greater Ranges...
