I got a customer that wants a few hedge type trees topped and trimmed up. I always forget the name of these things, but they're very abundant where I live in the Pacific Northwest. I've trimmed them many times, but my customer is talking about cutting these down to 10 ft. Right now they're at about 14-15ft. Am I in danger of killing these things if I take this much off the top of them? Will it be too much shock to cut 4ft off of them while also shaping them? I do a lot of Hedges, but I rarely mess with stuff much taller than 10 ft.