thats not a low score.. the highest is 7.0... and to get closer than what your score is becomes exponentially more expensive... and to be honest dont pay any attention to that score... it doesnt really mean anything.
Well, if it says 'please insert the disk and relaunch fallout 3' then yes you need the disk. If it doesn't, or just quits unexpectedly, then you've got a different problem. Did you install all the drivers, including updated drivers for your gfx card?
there is nothing wrong with the way you have it, infact, i would have the rear fan as an intake blowing on the cooler to help dissipate heat, if you have 3 fans in the top exhausting air you dont need the back exhausting the air
Personally I'd change the direction of the HS. If you swapped your back intake it'd compete with your front intake, effectively canceling each other out. Better to do a quick 90 degree turn with the cpu HS.