Sounds like a lot of hard work there Eric. If its any consolation, I'm digging out some large shrubs at present, one a Buddleja glubosa, the other a Viburmum tinus. Both were all of 10ft, so very large roots.
I wont be planting anything like that in their place!
Do you have that cutting down process every year? Dividing them would be a major undertaking, I expect, especially the Pampas grass.