I would be inclined to take out 2 of these 'ropes' down to 2 feet. When you see good new shoots growing then take out the others the following spring.

I agree with Volunteer though, my experience say you could hack the whole shrub back and it would still grow up like a weed. Our montanas' have obviously not read that t hey only need pruning back once a year at a specific time. They grow like weeds and get majorly hacked back as needed... and still flower like mad!

Thanks - this is very helpful. You've confirmed my inclination, but I'll do it with more confidence now!