All else being equal (in this case, quality of guns in question is the same), the amount of accuracy you need is entirely dependent on your own playing style. The more aggressive you are (and physically fit), the less accuracy at longer range you need (because you won't be at long ranges for long). Your height is also a factor, shorter people have problem with longer guns.
Also, to an extent, properly upgrading and fine-tuning a M4 can overcome any actual shortcoming of a M4's accuracy at longer ranges. A good hopup unit, hopup sleeve and tightbore will do amazing things.
Depending on your shooting style, battery size matters. If you shoot a good amount (1800rd+/day), especially on semi, you'll need multiple good mini batteries (or a single decent large battery). Semi is hard on your battery power because each shot is spinning up the motor from a state of full stop.
"The Bird of Hermes is My Name, Eating My Wings to Make Me Tame."