The rule of thumb all the Mods say for OCing is: EVERY single system is UNIQUE. So even if you and your brother bought the EXACT same parts from the same exact same place, your results will ALWAYS be different. OCing is based NOT JUST on the CPU, but the capability of the Mobo, the RAM used, the quality and consistency of the PSU and Power in your area (dirty power adds many more issues to the calculations), the type and performance of your cooling system and THEN FINALLY how specifically that INDIVIDUAL i5 was manufactured. All these things lead to how 'much' or 'little' you can OC. Someone using Liquid Freon on a specific Mobo, matching RAM, PSU, and of course cooling system got a iCore to get over 25Ghz!!! Could they maintain that? Only for testing purposes then of course shut down, not for game play. Yet I seen plenty of posts of people spending $2000-3000 for a system and the most they can eek out OC (as noted) was 4.6Ghz semi consistantly, and would have to lower down when playing some games or shut off OC when NOT playing, in order NOT to kill the CPU/RAM.
Remember OC is burning out your CPU faster (burning both ends of a candle) then the manufacturer guarantees it's performance / lifecycle will last under normal (40 hours a week 5 days a week) usage. More then one person 12 months later had to buy a new CPU because they kept pushing the OCing all the time, and well killed the life of the CPU that fast.