I have never bothered myself with R values, coat weight, etc but when I'm not wearing a jacket, I want it to fold up small and to fit comfortably in my rucksack. For me, it's all to do with what I wear and may need to wear depending on the weather conditions at the time. My clothes are now split into two groups, a general clothing group and clothing group specifically for when it rains. The following is all about dry weather clothing, nothing to do with keeping dry.
I don't like half zips so all my clothes are full zips. I also camp so depending on the time of the year, my general clothing tends to be, a base layer, a shirt or not, one, possibly two thin but warm cardigans (is this word now out of date?) a lightweight warm synthetic jacket plus my windshell. Now that I have a down jacket, I think in the colder months I will also pack this to wear and use when I've stopped walking, possibly to sleep in as additional warmth under my sleeping quilt, or to put on in the morning to keep me warm as I start to organise myself. The point I'm trying to make is that in my personal experience, depending on how you decide on which clothes to take with you, certain 'tricks' can be employed to decrease the clothes in your rucksack and lighten your load. For me I find the main 'trick' is to put on my windshell, once on I find I always feel much warmer. My down jacket is a stand-alone item, just to use when I need to be warm but not to use it to hike and then be sweaty in it.
At the moment my synthetic jacket is a cheap one from Alpkit, it does the job and for me is ideal to walk and sweat in.