FWIW, I chatted previously with 57mph about this and told him that I'd visited Feller, T&D and Shapiro this year and they all told me I was a candidate, yet the top of my head is what you'd call moderate diffuse thinning -- the donor area is not, though. I guess that is one major thing to consider.
But the overall advice here is sound, that you'll never really know for sure until visiting a clinic that can spend time with you face to face. I was impressed visiting the Shapiro group that they took time to do microscopic photos, counted hairs, calculated density, etc, so that we have much more clear, quantifiable data to work with in planning for the future.