Having a similar issue, however we are experiencing sever performance degredation almost to a point where users cannot do their work as our server is terribly slow.
Our issues started when i upgraded to esxi 4.2 u2 and the virtual machines to version 7 with paravirtual scsi and vmxnet3.
heres a typical output of my scenario
[3932] 87.0-88.0 sec 20.4 MBytes 171 Mbits/sec
[3932] 88.0-89.0 sec 26.6 MBytes 223 Mbits/sec
[3932] 89.0-90.0 sec 8.87 MBytes 74.4 Mbits/sec
[3932] 90.0-91.0 sec 10.9 MBytes 91.8 Mbits/sec
[3932] 91.0-92.0 sec 15.5 MBytes 130 Mbits/sec
[3932] 92.0-93.0 sec 8.10 MBytes 68.0 Mbits/sec
[3932] 93.0-94.0 sec 3.53 MBytes 29.6 Mbits/sec
[3932] 94.0-95.0 sec 3.63 MBytes 30.4 Mbits/sec
[3932] 95.0-96.0 sec 3.64 MBytes 30.5 Mbits/sec
[3932] 96.0-97.0 sec 24.9 MBytes 209 Mbits/sec
[3932] 97.0-98.0 sec 36.2 MBytes 304 Mbits/sec
[3932] 98.0-99.0 sec 41.1 MBytes 345 Mbits/sec
[3932] 99.0-100.0 sec 37.9 MBytes 318 Mbits/sec.
Very erratic and jumping below 30Mbits/sec. Im in the process of removing antivirus software (sophos) to see if that resolves anything.