I just found the manpage section Sven was talking about. This quote was a bit out of context because B.A.T.M.A.N. indeed considers the throughput when choosing the best gateway. This probably sounds better:
In level 1, B.A.T.M.A.N tries to find the best available connection by considering the gateway's advertised throughput as well as the link quality towards the gateway.
Is this batmand, not batman-adv? I'm working through batctl man page and have not found this text.
Andrew