I came to hammocking from an ultralight background looking for comfort.
In my mind, having a hammock that's too small defeats the purpose and will only save a couple of ounces. I still weigh the rest of my kit in grams.
Having said that, I don't think there is a singular answer to you question; and it's not because folks have individual opinions. I own three commercial hammocks and have made four DIY's. The two most comfortable ones are 48" wide and 67" wide - go figure!
I start out making my hammocks 11' long and generally find them comfy. However, just this past weekend, I made one out of crinkly parachute material and had to keep cutting the length down to get it comfortable and ended up with a 10'-4" hammock - go figure, again!
I'm becoming a believer that the material plays a very important roll in comfort, not just size. This Grasshopper is still learning the mysteries of hammocks