Current results on linux_amd64, 8 HT cores @2.4GHz:
BenchmarkTCPOneShot	   10000	    194037 ns/op
BenchmarkTCPOneShot-2	   20000	     93641 ns/op
BenchmarkTCPOneShot-4	   20000	     94039 ns/op
BenchmarkTCPOneShot-8	   20000	     94667 ns/op
BenchmarkTCPOneShot-16	   10000	    301924 ns/op
BenchmarkTCPOneShotTimeout	   10000	    193264 ns/op
BenchmarkTCPOneShotTimeout-2	   20000	     98247 ns/op
BenchmarkTCPOneShotTimeout-4	   20000	     94442 ns/op
BenchmarkTCPOneShotTimeout-8	   20000	     95297 ns/op
BenchmarkTCPOneShotTimeout-16	   10000	    307970 ns/op
BenchmarkTCPPersistent	   50000	     52050 ns/op
BenchmarkTCPPersistent-2	  100000	     29452 ns/op
BenchmarkTCPPersistent-4	  100000	     28823 ns/op
BenchmarkTCPPersistent-8	   50000	     30473 ns/op
BenchmarkTCPPersistent-16	   10000	    311777 ns/op
BenchmarkTCPPersistentTimeout	   50000	     32574 ns/op
BenchmarkTCPPersistentTimeout-2	   50000	     29723 ns/op
BenchmarkTCPPersistentTimeout-4	  100000	     28592 ns/op
BenchmarkTCPPersistentTimeout-8	  100000	     28997 ns/op
BenchmarkTCPPersistentTimeout-16	   10000	    314354 ns/op

R=golang-dev, alex.brainman, dave, mikioh.mikioh, r, iant, bradfitz, iant
CC=golang-dev
https://golang.org/cl/6458128