Again -Intel does NOT relabel CPU's.
Grossly over simplified explanation of how clockspeed is determined: A newly fabbed CPU is connected to a special "tester" machine. This machine controls all of the pins to the CPU, and specially-written test programs are played onto the pins (with expected results). The clock and voltage are increased until the point of failure, and this determines which bin it makes.
This is a very precise process and the result of this test determines whether the product is binned as a 2500k , 2600k, 2700k, or any other CPU. Intel does not simply relabel a 2600k to be a 2700k.
Its plausible that a 2700k could overclock slightly better than 2600k because it is binned a premium CPU with better voltage tolerances. Like you said , the difference is probably minimal but I'd love it if 2700k overclocks to 5ghz in the 1.3vcore range. That is nearly impossible for current 2500/2600k CPU's unless you win the silicon lottery and get the golden cpu.