The European Union has a standardised sleeping bag assessment (such things matter here). It is useful for comparison rather than as an absolute guarantee of comfort.
I would avoid any "system" with too many zips, these add weight and bulk.
I found the Ajungilak 3-season to be good for cool Northern European nights in Sept. I wouldn't want anything that warm in a heatwave or just a warm summer evening.
If you want to improve your warmth you should consider extra insulation underneath.