TBH in an everyday situation LN2 is no good to you as you would need to eitehr find a way to keep it liquid and in a closed loop system or keep refilling it , its great for one off record setting but for an everyday person in an everyday situation it would be useless to you
As For overclocking as thelis said it all depends on a few things
The ability of the chip , some geet up to 4 and more others may not so thats the luck of the draw
What ram you have and if you are willing to overclock your ram
And what temperatrures you are looking to keep the chio at , and what cooler you have
As for coolers i cannot personaly reccomend any as i have a AMD dual core system