well half truths ......
from what I been following on all the OC forums, the 2600k's usually hit higher OC's than the 2500k's....they often turn off HT tho.
If you are limited by heat, then having HT "on" will mean about 7C. If ya have a good cooler.....this is going to be less of a concern.
On the 2600k's, I usually set them up for everyday boots at 4.6 Ghz w/ HT ON under one BIOS profile 4.8 GHz to 5.0 Ghz w/ HT OFF
On 2500k's I get mostly 4.6 to 4.8's unless i start turning stuff off. If ya use offset method, you will downclock when load drops....but ya can get higher OC's using fixed numbers.