It depends on how much climbing you are going to do and what cadence you prefer. You can always keep different cassettes on hand and switch them for different events. I'm 200 pounds and I climb a lot and I have a 34x29 low gear but there are times I wish I had a bigger cog back there. 50x12 high is enough for most situations for me. I don't race but I don't like being spun out on rollers or descents.