I really like the old discontinued Easton 4mm Carbon Injexions. 330 spine in my case. Been using them since 2013 and have enough to last me quite a few more years. Killed a pile of animals using them including a real nice Mt Caribou and good Black Bear this year.
I've shot Elk, several Caribou, Stone and Dall rams, Polar Bear, Brown Bear, Musk Ox and a couple Moose with them besides Deer and a lot of Black Bears..
The shafts as well as the components I use have proven very durable. I install the provided D-6 22 grain weight stainless steel insert to stock depth using Easton provided epoxy. That D-6 insert is just for reinforcing and a bit of FOC. I do NOT like D-6 components as they are thin and weak vs regular components....so use Firenock outserts so I can utilize regular 8-32 threaded broadheads and field points. With a 4" wrap, regular Easton nock, 3 helical Blazers and a 100 grain broadhead my arrows come in at about 471 grains for my 29-5/16" draw length 65# bow.
Good luck to you and your 4mm shafts. I like 'em!