Your NAS could also be a bottle neck... if you use your NAS for more than storage ie. streaming and stuff, I'd also highly recommend:
Got this for a £85 with HP's £100 offer; 4 - 5 bay, eSATA, RAID controller... tis great. Getting around 80-100MB/s wired from PC :)
Already 15GB gone... fully settled at about 90Mb/s for 2hrs+ a major improvement over my previous NAS which I could only get about 30Mb/s to MAX.