Sounds like it is having trouble negotiating the speed properly. What brand nic is it? It could be a bad cable, the laptop nic might just be more tolerant to a bad cable.
Try plugging your computer directly into the modem and test it.
This will prove its not the router.
If your connection is still low it may be the modem itself or the lines, or network saturation ( remember most ISP only promise up to the advertised speed).
When are you doing speed tests...
Except firefox has threading problems with more then 30-40 tabs open and it pukes and on itself, chrome might be a memory hog but you can get up past 100 tabs open.
Those are all fair points.
I got a new job and I kinda want to try one of those 90 degree silverstone fortress cases, they all seem to be MATX thou, bummer.