How to calculate CFM if a fan is filtered?

[CosmosVacuum]

Hello everyone! I'm building my programming and gaming PC, I only play Dota 2 and LoL but will compile a lot of code. I will run this PC 24/7 so I need a good cooling system (good but not expensive because I'm on a budget). Here is my rigs:

• 
  CPU: Intel Core i7 6700
  HSF: Cooler Master Hyper TX3
  GPU: MSI GTX 750 Ti OC 2GG
  MBO: MSI B150M Mortar
  RAM: Kingston HyperX Fury 2x8GB DDR4 2133
  SSD: Samsung 850 EVO 250GB
  HDD: Western Digital Caviar Blue 1TB 7200RPM
  PSU: Antec HCG-520M
  CAS: Cooler Master N200 Windowed, included 2 x CM XtraFlo 120mm
  And 2 more 120mm fans for this chassis

After a bit of searching I've found that this XtraFlo fan has 82.9CFM and 2.7mmH2O. I'm going to put 2 included fans at front (intake), so I'm going to find another 2 fans to put at rear and top of the chassis. I wanna create a sightly positive pressure environment inside the chassis because I don't want dust build up so quickly. In theory I need to buy 2 fans that has sum of CFM < 2 intake fans' CFM, but my intake fans have dust filter, so I'm confusing about choosing exshaut fans.
Which specs (airflow in CFM and pressure in mmH2O) of fan should I looking for, to create a sightly positive pressure environment?
Is there a way to calculate CFM (or mmH2O) of a fan which has dust filter attached?
(I will connect fans directly to PSU, let them run 100% rpm all the day)

 

[Lutfij]

1| Are you sure your ears can tolerate a fan that has been running at 100% for everyday computing at 24hours usages per day?
2| You may want to read through this article on Caselabs.
3| Are you sure you want to go with a positive case airflow inside that case? I've worked inside it and the thing I've learnt with Coolermaster cases is that they are good for airflow not for negative or positive pressure since their case designs aren't that way. Silverstone are revered for positive case pressure and their designs are reflected in them.