I've played around a lot with.
Here is what I found, if you add weight to the bottom of the gun (ie. tungsten magwell) It shoots REALLY soft and is very stable, but it doesn't return to target as fast. To make it return at the speed I liked I had to use a 16 lb spring, which caused other things that I didn't like to happen.
Feel is what it is.
I know I can get to the next target as fast with a heavy or light gun because the timer tells me so. I think the most important thing is that you are comfortable with what you are shooting. Some like light violent (i.e. Glock) guns and some prefer softer shooting tanks, both are better than most any of us will ever be.
So, make something YOU think is cool and don't worry about the rest, and most of all feed the thing as much and as often as you can. DVC