Mine has become my main shotgun, save for deer hunting. I've used it exclusively for grouse and pheasant for the last three seasons. It has performed perfectly thus far. It is a 16 ga and weighs 6-3. There are few of the 16's that are that light. Most are over 6-8 and some well over 7, especially when the pad system is installed.
The 20's range from the lightest I've noted at 5-14 to 6-10, most right around 6-4. I am sure there are some variance either way from these.
I have to ask why you are not confident in your 28? It sounds perfect for grouse!
Chief