The OverClockers BSOD code list

[Sam_oslo]

0x 124 is definitely not VTT. Bumped Vtt and still got one. It passes IBT, LinX and will BSOD 0x124 idle or surfing. 2500k didn't do this, extremely frustrating.

It's not vCore, specially when you are using manual vCore. Because when it passes IBT, LinX, then shouldn't BSOD at idle.
It's not you RAM either. Because it's working fine with 2500k, assuming you are using the same RAM and settings.
The next candidate, and most probable source of problem is the IMC.

If that 2500K is doing fine wiht same MB and same RAM, with same settings, then probably the problem is the IMC of your 2600k.

Adding more VVT/VCCIO should help, but UnCore runs at the same speed as Core on SB, and some IMCs seams to be having problems at x50+, no matter how much juice they get.