Make sure both devices are negotiating at 1gb. PCs in general have tendencies to not refresh network mappings unless you are constantly accessing the NAS/WHS.
I currently have two ReadyNAS Business Pro, and although the sequential write/read speeds are sustained at 85Mb/s, I currently finished building my HTPC/NAS. Does your NAS/WHS have dual NICs? If so, you should bind them so you can get more bandwidth.
