Ethernet Cable; is there a practical limit to the length of run, are repeaters (hub) needed to amplify signal?

I'm running my DSL out to my shop which is about 150 ft away from my house. I have a pre-n router, and the signal is at about 50%. I can move the router about 50 ft closer, if I run 100 ft of RJ45 cat. 5 cable. I was considering cat 6 but the cost is considerably more. Is there a limit to how far a patch cable can run, given that is carries no current, would the signal be affected at 100 + feet?