Really it's up to you. I love my Salsa Fargo for the comfort and stability. Carbon bikes are great and fast, but I felt every bump and when the wind or a semi truck came by, I felt like I was being blown off the road. I feel much safer on my steel Fargo.

I would try out both materials and see what works for you.

I would say carbon is faster, but I do just fine on my Fargo. Salsa and Surly make some really great steel bikes but don't have the components you are looking for. My next steel bike would probably be a Surly Cross Check. If you have dealers in your area, check them out. You can also build up a Surly or Salsa to your specs as well.