Surprisingly I've never seen any recommendations on here of the particular setup I use, but I use all-purpose DWR outer softshells in weather down to the mid 30s (daytime). I no longer carry raingear, and I seldom carry an insulating layer for around camp or sleeping. This setup allows me to carry spare baselayers if I find it necessary.
I wear a pair of eVENT shoftshell pants that wick rain with ease, but aren't as friendly as traditional raingear when you put body weight on them (ie. sitting down on a wet log to adjust your shoes).
I also carry an old Marmot softshell which is heavier than I would like, that also has a DWR exterior (not sure which DWR), but I've never had a problem with wetness -- not even with a heavy pack putting weight down on my back. Of course the jacket has an attached hood as well.
Obviously your question was about traditional raingear as a sole outerlayer. Personally, I would not use this approach in temps in to the 30s because raingear has major breathability issues with no insulation. I don't like the idea of sweating in the cold with no insulation other than shorts.
Wearing full baselayers with just raingear would be another approach that I have never thought of; but I still don't think I would risk it down in to nighttime 20s.