the reason the connection drops as low as 54 in some areas of the house is that the newer wifi protocols dont have the same range/signal strength as the older protocols but they have increased speed. you are probably on portocol G when further away from the router.
Your wifi speed will also depend on how many devices you have connected to your router, as they all split the "theoretical" maximum speed of the wifi. I say theoretical as i have never come across a router that actually provides the theoretical max speed, even when only one device is connected and it is right next to the router. If i remember correctly the maximum theoretical wifi speed your laptop(N wireless card) can handle is 480Mbps but that will depend on your router also.
As a fellow mac user i can tell you that you wont get the 130Mbps you are currently getting on many other laptops with wireless N card or even newer wireless cards as Macbooks are build with many wifi aerials. I have tested mine last year vs a brand new dell laptop and a new asus and my 5 year old macbook beat them all for wifi speed. I was getting around the same as you while the others were only getting 30-60Mbps
what kind of router do you have?
