Acctually not so important because I usually use some passively cooled low budget graphic card.
I will probably buy Asus R5 240.
I'm not a gamer. The machine is for raster and vector graphics and for movies.
For a GPU this low, if you have some airflow i bet you go fanless, specially into how massive the MK-26 is. Im not too sure, but from what i seen this are half sized, not sure if the MK-26 would fit though, or is it safe. Either way, as i said earlier, i have no experience with AMD cards into aftermarket coolers and if they can control standard PWM fans, i know that Nvidia can't at least with the included prolimatech 4pin pwm gpu adapter to 4pin standard pwm fan, but i have not seen complaints, so im guessing AMD has a more standard PWM design, so might work.
1. Which 2 PWM fans for Prolimatech?
Really depends into how you want to control them, or if the GPU is capable of controlling PWM fans or not. But lets assume it can, my first pick on PWM fans on 120mm would be Noctua NF-S12A PWM due to its range of operation, they can drop extremely low or ramp up as you set them up. I leave you a graph of an NF-S12A PWM ran on Asus Maximus VI Gene on a CPU_FAN (true pwm fan header) that its tested with FanXpert2,
My first pick on 140mm fans, would be Prolimatech Ultra Sleek Vortex 140mm x 15mm Slim Profile PWM Fan - (120mm Mounting Pattern)
, they are slim so will not weight as much, they have good static pressure (search the web you will test vs multiple fans), they look good (at least i think they do), and they have a good range of operation controlled via PWM, you do need to get the special mounting clips Prolimatech Ultra Sleek Vortex 14 Fan Wire Clip Set - MK-26 Series
. I leave you a graph on fanXpert2 for you to check the range of operation. it should idle around 450rpms (if the cards allows it).
Now lets assume it wont work with PWM, so you wont be able to control them via the GPU vbios or software. Then my pick would a ver low RPM 120mm fan, Scythe Gentle Typhoon 120 mm D1225C12B1AP-11 (500 rpm)
, wonderful quiet and they have real ball bearing so they shoudlnt have issues with horizontal placement. Although you wont be able to control them, i leave you the graph on FanXpert2 just for you to know you can still undervolt them if you wish.
As a last option since you like phantek, personally i feel they are very good quality and decent sonic signature, but on PWM they dont go as low as noctuas, the lowest the Phanteks 140mm Case/Radiator Cooling PWM Fan (PH-F140XP_BK)
can go is 600rpms, also they will weight putting more strain on the gpu. I leave you a graph of it,
2. Does it make a difference if I put 2x120mm or 1x120mm + 1x140mm? Speaking of RPMs as with 2x120mm I'll get equal RPMs and with other option the RPMs will be different producing unequal frequencies, possibly producing new unwanted (maybe louder) frequencies?
All fans have different characteristics, not to say difference in size, but chose carefully and a 120 or 140 can be as quiet, the 140 having the advantage of being bigger needing less rpms to move equal amount of air (if all others variables are constant), and in 120 the advantage is that there are a lot more options to chose from, specially since you care about the looks. But overall there are good options for both, so really wouldn't worry too much about this.
My first choice would be Phateks.....I would avoid Noctuas due to ugly colours. Any other choice?
As Quest already posted, Noctua now has recently introduced other color options, to what i remember there is a grey NF-S12A PWM and a black NF-F12, check Noctua introduces two new fan product lines and accessory kits