Which fan should I use,120mm or 200mm??

[manasthakur1224]

I'm having this Cooler Master "HAF 912 advanced" & I could either go for 2*120mm or 1*200mm fan at the top. Reason being I've got just 2 stock fans, @ the front & the rear & one "CM Hyper 212x". Though the temps hover around 60-70 degrees, I still feel there should be one(or two) more fan(s) installed.
Now,I'm not even sure that if there's enough room @ the top & could an additional fan be adjusted @ all as I'm not much into building PC's & opening & putting parts together, so I'm attaching the pics here to find out if its possible & if yes, then what combination should i go with?
http://i66.tinypic.com/2dr5pp2.jpg
http://i63.tinypic.com/2i1le34.jpg
http://i67.tinypic.com/zvbmll.jpg
http://i64.tinypic.com/24q2yih.jpg
http://i68.tinypic.com/2i1cln5.jpg

 

[JQB45]

1, 200mm fan should be quieter then 2, 120mm fans - and put out a good amount of air. Try looking up different fans and comparing the amount of air they are rated to move.

 

[manasthakur1224]

1, 200mm fan should be quieter then 2, 120mm fans - and put out a good amount of air. Try looking up different fans and comparing the amount of air they are rated to move.

Even I'm inclined towards a single 200mm fan,its just that i don't know if the fan would fit, I mean it can certainly fit as its shown over the HAF 912 box but I just want to make sure that the positioning of the RAM & CPU cooler won't make it tough to install a fan @ top & hence i send the pics in links above.