[Berties]

Looking at the two computers, if I were to replace the fans

HTPC
two x NF-S12B ULN (case and for CPU heatsink) £17 each

Gaming rig
Five x NF-P12 PWM (case) £12 each. 19.8dB

Compared to Xilence 12cm fans at £4.66 each 21dB. Is it worth spending the extra?

Unless decide just to go for a single Noctua on the HTPC case fan (that is the loudest) and go for Xilence all round on the gaming rig.

right moved the Noctua 12cm from the gaming rig to the HTPC with the blue speed reduction cable. Quieter than the Antec tri-cool as that made a slight motor drone sound. HTPC is very quiet now.

Just have to decide whether replacing all 12cm case fans plus the Antec 12cm to Xilence. Replacing all with Noctua will be a bit expensive.

[dhicks001]

Really it's up to you but I would if I could. It's also knowing you have the best fans you can get and when you tell people you have noctua fans they instantly know you have good fans in your case. It's worth noting though that 4/5 fans will be louder than the rated noise as there are simply more of them. Unless you use the speed reducing cables to slow them all down.

[TastyPC]

Don't know if your still wondering about Noctua fans but I've made a 120mm fan comparison video. It doesn't cover the Xilence fans but should give you a rough idea what the noctua fans (NF-F12s in this case) can do/ sound like.

120mm Fan Comparison Corsair H100 including Noctua NF-F12 and Silverstone AP121 - YouTube

Might help you little in making your decision.

In my opinion they are worth it.

Have you considered the Silverstone AP121

[5teviewonders]

Wow!! She's hot. Here's another fan comparison. Noiseblocker fans seem to do quite well.

[M] 120mm Fan Roundup - 35 Models Compared