By run for I meant how long it will be turned on with out being shutdown.

As for sound this does matter with headphones. Trust me, the computer next to me can be heard though walls and doers to the other side of the apartment. If sound really does not matter getting it to 4.0 is easy as all you do is buy the biggest baddest fans you can afford and a decent heat sink.

Here is what I would recommend to get 4.0+ where sound does not matter:
http://www.frozencpu.com/products/78...?tl=g36c15s780 Exhaust fan.

http://www.frozencpu.com/products/70...?tl=g40c14s757 Heatsink

http://www.frozencpu.com/products/85...l?tl=g36c15s60 Use this fan on heatsink instead of the stock one

http://www.frozencpu.com/products/37...?tl=g8c127s447 Thermal paste

That should get you to 4.0 easily all within your budget. It should also come out quieter than my current system as you are only going to use two loud fans. But yea, that will cool it easily... all within budget!

(Note that you can find most of these parts for less at other stores, prices here are maximum)