All cpus are different and have a different "wall" as to their top overclock speed. Take it as he got strong chip that can handle it whereas some just cant reach that point, thats why people dont just copy others overclock settings. Maybe try more fine tweaking, i never oc'd a intel cpu b4 so this is where i leave u lol.
And 4.6 on that ivy bridge i5 compares to roughly a 4.8,5.0 sandy bridge 2500k, and wouldnt consider the worst 3570k ever. I know that IB requires less of an OC to reach high OC of SB but not sure on exacts.
Also some motherboards help overclock better, ur brothers motherboard is this websites recommended buy if i remember correctly, not saying that the ga-z77x-ud3h isnt good, but in the case of overclocking the motherboard can limit ur OC.