For LAN replication over GBE or better, the defaults and Open-E are already optimized. HOWEVER.. you may not have enough memory. IMO, at least 8GB is a good starting point depending upon your workload ESPECIALLY when replication is involved.

Jumbo frames isn't just about throughput. It's to reduce CPU utilization. Larger frames means less interrupts being generated. What kind of performance degradation did you see when enabling them?