From my experience in consulting doctors in person and online for the coverage you want and require FUT is the method for a megassion over 3000 grafts.
You need to be concerned with your donor area. If you do a 5000 graft FUT, it may be in the cards for you to do an FUE in the future. To do a 5000 graft FUE
may result in donor over harvesting. I did a 1250 graft FUT to the hairline 5 years ago and am happy with the result now I want to touch up the hairline and address the mid scalp and crown. Several have recommended 2500 grafts FUE, original doc has recommended 3000 grafts FUT. Hasson recommended 2500 grafts but will consider a 2 day procedure based on seeing my donor area in person and I could get another 1000-1500. Im 59 this is the last procedure I want to have so I will go to the max as long as my donor area is not over harvested