Hi Ingvar,
The maximum ports you can achieve when using split options is 64 (with a mix of 40GbE and 10GbE).
If it is a gateway, you need allocate some of the ports to run as FDR, while others to run as Ethernet. It could be 50-50 (%), but not necessarily, it depends on the setup being used. it is possible that you have more hosts on the InfiniBand side or vice-versa.
This post may help as well.
http://community.mellanox.com/docs/DOC-1450
Ophir.