I've yet to see a reference showing how thick a graphene space elevator would need to be. That doesn't mean there isn't such an estimation, but that I simply haven't seen it.
That, and if I were better-educated on how to calculate the tensile strength required to maintain a 42,000-mile graphene cable while multiple multi-ton loads were traveling up and down its length at varying speeds at any given time, I'd happily do so. But I'm not. If you are able to present such a calculation, then please do so.