It's been a while since I did the overclock for my i5-2500k system... One thing to keep in mind is that when you change between 100% full blast and idle the core voltage also ramps up/down. This can be a fun puzzle when your system is stable running full load, and then suddenly hangs when not doing much at all. So first off you want to change the core voltage to something fixed, and then see how fast you can get it to run in a stable way. Oh yeah, and keep memory clock at stock funtil you find out what the core can do... You want to test one thing at a time.
Just did a quick check of my notes (well, spreadsheet) ... Make sure you use a manual Vcore mode, not offset. Offset mode can give you surprising values for your core voltage. And only for the highest overclocks did I need to bump VDIMM a little. So for 4.8 and 4.9 GHz VDIMM was bumped from stock (1.500 Volt) to 1.550 Volt). And FWIW ... VCCSA also needed a 40 / 60 mV increase for 4.8 / 4.9 GHz respectively.
The above is without any GPU related load, since I only use the overclocking for fpga PAR runs which take too frigging long.
Oh yeah, one thing I remember ... depending on the particular chip you get you may or may not need to bump the PLL voltage a tiny bit. Apparently I got lucky and just used stock voltage (1.80 Volt).
And for the rest I'd say google for "Ivy bridge overclocking guide".