Something as high as 4.2 on these Phenom II's C1E needs to be disabled, 4ghz its hit or miss, but C1E for sure needs to be off, Cool n Quiet is nice when your idling, it will lower the clock to around 800mhz - 1200mhz during low load, This probably wont be an issue, but can cause some stability problems in the voltage area on some boards.
The 965 I OC for a friend could hit 4.1ghz with Cool n Quiet enabled as well as my 1100T at 4.2
http://valid.canardpc.com/show_oc.php?id=2461122
4.2 is sometimes hard to get on a Phenom II CPU, some times you can get lucky and get 4.5 or so on them, But let me tell ya, these things warm up when the volts get past 1.4v. Best Overall OC would be to raise the CPU-NB no lower then 2500mhz and voltage no higher then 1.3 on the CPU-NB and keep it at 4ghz(This give a really noticeable performance boost on Desktop and on games). I lowered my OC to get my CPU-NB to 2912mhz, Im sitting at 4ghz right now but with a higher CPU-NB. Just make sure you have the cooling for it, like I said, these things get hot after 1.4v. Max temp on these are 62c, Use Prime95 to stress the CPU for a few hours, make sure you don't pass 62c, system will lock up at 70c to prevent it from hurting the CPU.