As most of us who have DSL know, it is a vulnerable technology. Speed can be affected by an array of factors. To get the best speed out of a DSL connection, all telephones on that same line should be filtered. The best way to have your DSL wired is with twisted pair wiring (i.e. CAT3, CAT5, etc.) directly from your NID, (network interface device) which is usually a box that is placed on the outside of your premises where the phone line from the pole or ground makes a demarc point between telco responsibility and customer resposibility. Twisted pair wiring enables your connection to be less suceptable to frequency lost, which basically means an optimal DSL connection. You want to make sure that your phone cord is as short as possible from your DSL modem to the wall jack. Just that information will make for the best speeds. Also, a good cat3 (twisted pair) phone cord will help out a lot. You also want to make sure that your DSL modem is not too close to any sources of interference such as computers or other electrical equipment.
Also, an external POTS splitter would be optimal if you have many telephones. This device basically lets you run any telephones to a device placed next to and wired to the NID. You can run a dedicated Data wire from this device as well. More information on POTS splitter installation can be found at www.dslreports.com or elsewhere.
I'm not sure if this information will help anyone out. This is all in regards to any physical connections and how they will increase reliability and speed for DSL connections, in most cases. I work at an ISP that provides DSL access and let me tell you, these few things do help.