Some Fan Questions.

First, I've got 2 cpu fans that I plan on replacing sometime soon. They are CoolerMaster Blade Master fans, and they are attached to the coolermaster hyper 212+. They are 120mm, and they have a maximum rpm of 2000. I'm looking at the Noctua NF-P14 FLX. It measures 140mm, but should fit where a 120mm fan was or would be. Maximum rpm of 1200. Now, I'm not sure if the fans I currently have installed are too powerful (together, that is), but I would rather be safe and go with something that is somewhere near the same. So I am considering those Noctua fans, two of them, but I don't have cfm data, only size and rpm. So I would ask the community what rpm would the Noctua Fan's hypothetical 120mm sized equivalent (in cfm) have? And if I switch to the Noctua fans, would I see a significant rise in temperature? Or, considering that I do and would have a dual fan setup, then, in praxis, would the difference between the two be mostly in the level of noise?

Second Problem. The chassis is a Lian Li PC-B25F. The front 2 fans are 120mm, and I am considering using the same fans as above, but I am worried that the rounded frame's of the two fans will be so large that they will conflict with one another. Has anyone ever tried replacing two 120mm fans that are similarly close together with two Noctua NF-P14 FLX fans? If not, then maybe someone could take a look at the pics and specs and tell me if I will have problems.

Third is a similar problem. I have a single 120mm rear exhaust that runs at 1500 rpm. I do not know if the Noctua NF-P14 FLX will fit. And I am unsure if the added diameter would be superior to the NF-P12 -- that is to say, I would like to know if the added diameter will improve airflow when that extra room in which the fan maneuvers is blocked by the chassis. And I am also questioning whether any of the Noctua fans will be powerful enough to replace my rear exhaust. In case it matters, I do (and will) have both cpu fans blowing right into the rear exhaust, so that will sort of assist the rear exhaust in expelling heat, right? So, I'd like to know whether I should replace the rear exhaust with a Noctua fan, of a specific type, or whether I should look into a different fan? If the latter, then some suggestions would be nice. I do not want to have one fan that is too much louder than the rest, as that would kind of defeat the point of using sound-optimized fans everywhere else.

Thanks.