I'm 6'5" & my weight has been over 19 stone in fairly recent history, but currently around 15 stone. I rode a Spesh Allez for many years with no issues on the frame, wheels & BBs were the weakness for me
A few years ago I bought a carbon bike from Planet X, frame cracked on the downtube just into the 2nd year, they replaced it with no hassle, then the 2nd frame cracked after a month & 500 miles on the seatpost tube
Had a right hassle getting that sorted under warranty. Sold the replacement on, as while I was waiting for it, I bought a Van Nic Ventus. It was a close call for me as to which was best, as they were both slightly different, but on longer rides the Ti edged it for me. Now I have the Van Nic & an Enigma Etape alongside it
If I were to buy carbon again, it would be from a local shop & from one of the bigger names with a good warranty, but TBH I think I'm a Ti convert now
I've not ridden on a really good steel bike, so can't compare steel & Ti. I was going to ask to test ride a steel bike down at Enigma, but apparently I'm not allowed to spend that much on a bike again, so thought the test ride was pointless