No, I am not using Jumbo Frames. In my Lab Environment there ist only one HP 2810
Switch with 2 VLAN's (one for Mgmt and iSCSI and the other one for Replication).

OPEN-E Network Test Tool shows 90-94 MB/Sec Speed on the Replication Interface.
Astonishingly Replication on the same Interface works like a ISDN Connection.

Testing with Crosslink Cable is a good Idea. I will do this an report the Results.