can rj11 cable slow connection speed?

I need as much speed out of my cable as I can get. Haveing cable installed today (lightning roadrunner) with brighthouse. Cable guy says rj11 will be too much speed at the modem as the meter coming out of the wall shows +6. Is he being straight up or trying to avoid the extra expense and or work? Can a broadband connection be too fast? I will be running 2 i7s 2 quad4s and a few laptops at the same time. The dop from pole is about 150 foot and there is an aditional 50 in office before it gets to the modem. Thank You for any help you can offer as he is gonna be back with the rj11 cable within a couple hours.:confused

 

RJ11 - 4 wire "phone cable"
RJ45 - 8 wire "ethernet"
RG-58/59 coax "cable"
So first his terminology is off, and yes distance does degrade signal, how much depends on the signal strength & the quality of the cable & the distance.
Plus the cable company can add a booster.