Depends on the type of load and disc used. For random reading can be cases when it will not give 300 Mbps with clogged completely Orami.
Secondly, 4GB is the entry channel of FC to the receiving host. What the host does with the discs and what he is bringing into the network are very different things, because a lot of intermediate buffers.
In General, you have the theoretical limit of the bandwidth of the FC link, and you're asking about the bandwidth of the Ethernet channel which will be connected via an intermediate server. There are too many uncertainties between them. Testrite.