By far my favorite jacket is this Canari jacket. Mainly because the back zips completely out allowing lots of moisture removal after warming up.
Good for upper 40s down (with a thin long sleeve jersey underneath). Works great down to upper 20s when paired with a thicker winter jersey.
It is called the Eclipse Convertible and the sleeves zip off too to use as just a vest for temps in the 50s.
+1 for the back vent. your post about the back vent got me curious so I checked my Novara rain jacket that I got on sale at REI off season. turns out it has a permanently open transverse high back mesh vent that is always open, pit vents w/o zippers that are always open, and a nifty large back zip pocket which was great and easy to access for my clear shower cap for easy on and off depending on body temp/weather conditions. the back looks kinda like this one. I added reflective tape to mine.
Originally Posted by love2pedal.com
The Showers Pass Softshell Trainer is a nice option. Has nice ventilation with 2 core zips and a rear neck zipped ventilation port. Good waterproof material as well