The Firestorm cores are capable of issuing two 128bit stores per cycle [1], giving a bandwidth of 102.4 GBps. This matches the experiments by Andrei with mixed reads/writes [2], and I have personally verified that it is attainable for pure write workloads to L1 as well as L2.
This does not mean 102.4 GBps is achievable on a single core, but if L2 bandwidth is the limiting factor it very well could be.