Each person brought 5 bags * 50 pounds per bag = <<5*50=250>>250 pounds per person.
There are 6 people * 250 pounds per person = <<6*250=1500>>1500 pounds of luggage on the plane.
The plan can hold 6000 pounds - 1500 pounds = <<6000-1500=4500>>4500 pounds of luggage space left.
The plane can hold an additional 4500 pounds / 50 pounds per bag = <<4500/50=90>>90 pieces of luggage.
#### 90