5cm.. that's defo a replacement. most car insurance igrone windscreen claims or have their limits set to something really stupid high before it affects your ncd.
I had one that was under 1cm, it had not spread but was more of chip out of it. it was about 10cm from the edge and the "AI" system wanted to replace it and booked me in for a replacement.
When the bloke came to my house, he was like... I speak to my boss about repairing it, it was an ok job; I could still see the mark; if I looked for it. but the car when to the scrappers 2 months afterwards (poor girl) and it was £100 pound saved.