My bad. Her speed is only 515+50x5=765. 50x5 is how much her 2nd skill add to a squad of 5. I usually do that to sort speed (e.g Red Ranger is 700+150x5=1450, Onicidium is 635+100x5=1135)
OK so you're saying the "+50x5" is like adding 50 to each of the 5 girls, instead of averaging and then adding 50. Just a different (and perhaps more clear) way of showing how the girl buffs her team's speed.