"I had found that esxi had very slow network performance"
What do you consider slow?
I am seeing 800Mbps + testing with iperf, and 70+ MBps file copies from guest os to my workstation on esxi 5 running on a cheap ass N40L box
Now what is odd, is I see 400mbps to pfsense with iperf. But since its only got a 20mbps internet connection doesn't really matter that much