Sounds like your limitation is disk speeds not network speed. I have a Gbit network here and get between 60 and 90 MByte/s sustained depending on which system is doing the writing. This is as determined by real life transfers of either movies (between 1 and 4GB on average), or music files (10MB or so on average). Oh and this is all on actual physical systems, not VM's. As a rule btw, the bigger the file, the higher the transfer speeds (sequential reads/writes being the cause of this; much more overhead for lots of little files)
All your figures are in Mbits/s not MBytes/s so a lot slower. Not sure how the virtual nature of your setup influences this. Also, I have jumbo frames enabled on all my gbit nics, set to the highest common value. Prior to enabling this I was not getting more than about 50 MByte/s.