hope i am not repeating any known article i missed on google

My architecture is as follows
2 esxi servers with 1 nic for management and 2 nics-lag for san (ISCSI)
1 netapp storage with 3 nics-lag for san (provides storage for esxi machines)
1 VEEAM AND VCENTER Physical server with local disks in raid 6 as backup storage with 1 nic for san (connected to iscsi and shows esxi datastores physical luns from netapp - offline as described in manuals) and 1 nic which is connected to the same network as esxi management ports this server is also the proxy (it is very strong)
my bottleneck is 99% source all others are under 20% - my backup usually runs at 85mb/s
i have one free nic -
the question is
to improve performance - should i create a lag on the iscsi nic which reads the data in san mode from netapp, or should i lag the lan nic which talks with esxi on management nics?
hopefully my question and architecture is understandable enough, and maybe someone can give me an answer
thanks in advance
nadav