Best fans setup for NZXT s340 elite?

[IT_Noob]

So my "problem" is as follows:
I've set my GPU fan curve so that fans don't spin below 30 degrees, then they start at 30%. The problem is that when I'm not doing anything demanding GPU power(such as browsing), it's temperature is going from 29 to 31 degrees. This makes fans spin fast and loud (they go above 30%) for a few seconds, then they go down to 30% and eventually turn off. The cycle repeats and its annoying.
I don't have any intake fans, so I think if I add one I'll get rid of this problem. My case comes with 2 exhaust fans pre-installed. Rear supports only 120mm, while top both 120 and 140.They're NXZT FN V2 120mm fans. I'm planning of getting noctua ippc fan(s). But I wonder what would be the best to do:

1. intake - 1 x Noctua ippc 140mm; exhaust - FN V2 fans default config.

2. intake - 1 x Noctua ippc 140mm fan, 1 x FN V2; exhaust - 1 x Noctua 120mm(rear), FN V2(top).

3. intake - 2 x Noctua ippc 140mm fan; exhaust - FN V2 fans default config.

4. intake - 1 x Noctua ippc 140mm fan, 1x FN V2; exhaust - 1 x FN V2(rear)

I kinda don't like the last option, because I think more dust will come inside as there is no fan at the top, am I wrong with that? Also should I go with 2000 RPM or 3000 RPM version (same price here)? Yes I know they 3000 version will be louder above 2000RPM, but at lower RPM they should sound the same right ? Which means I don't have reason to go with 2000 or do I?

 

[Aeacus]

I'd go with option #3 and get 3000 RPM fans since you can always run Noctua fans at 2000 RPM or less but you can't run 2000 RPM fans at 2400 RPM, if you need more airflow.

Also, with 4x fans (2x 140mm intake + 2x 120mm exhaust), your case would have optimal airflow which would be tuned somewhat towards positive pressure.

As far as GPU goes, my MSI Gaming X GPU has a fan curve where fans doesn't spin when GPU is below 60°C (Zero Frozr). Due to this, my web browsing is nice and quiet. With that, you might want to set new temp target for your GPU as well, e.g 35°C.

 

[IT_Noob]

I'd go with option #3 and get 3000 RPM fans since you can always run Noctua fans at 2000 RPM or less but you can't run 2000 RPM fans at 2400 RPM, if you need more airflow.

Also, with 4x fans (2x 140mm intake + 2x 120mm exhaust), your case would have optimal airflow which would be tuned somewhat towards positive pressure.

As far as GPU goes, my MSI Gaming X GPU has a fan curve where fans doesn't spin when GPU is below 60°C (Zero Frozr). Due to this, my web browsing is nice and quiet. With that, you might want to set new temp target for your GPU as well, e.g 35°C.

I've tried picking 35, but it will reach them and same will happen, I know I could go higher, but 60 seems too much for idle to me. As for 3rd option, would these NZXT fans really be able to exhaust enough?

 

[Aeacus]

Since stock NZXT fans can do 45 CFM, they are decent airflow fans, but poor in static pressure (0.9 mmH2O). Though, there are worse and better fans as well, e.g Noctua NF-A14 IPPC 3000 RPM at max speed, delivers 158.5 CFM. Then again, that Noctua fan is one of the best out there.

If not enough air is exhausted, then you'll get positive pressure. While not as good in cooling as negative pressure, you'll get much better dust management. Also, you can match your Noctua speed/performance with your NZXT fans performance for neutral pressure.