If you'd go back and actually re-read the previous 4 pages, those question have already been answered.
We already stated that an M16 will be slightly more accurate at range than an M4. We can't tell you by how much, because it depends on a lot of different factors (hop-up, BB weight and quality, etc.).
And M16 can be converted to an M4 and vice-versa, but I wouldn't recommend it.
The front foregrips on M4's and M16s are fairly modular and you can swap them out with different ones.
"Someone in a Prius tried to race me at a stop sign the other day. I couldn't believe it. I had him for the first 100 feet or so but I can only walk so fast."