My impressions with the 150x50 Delta's:
- They are H U G E. Measures are only measures, seeing one in person is a whole other thing - let alone 6. Not only they require a lot of space, but their mounting is not-standard. I recommend to use these only if you have a lot of velcro and huge 140mm cut-outs on your case, or if you are well-versed with modding it and making custom cut-out and holes/adapter.
- Their startup noise/rpm is okay-ish, they don't go as nearly as low as the AFB1212SH's I also have which can go down to less than 500 rpm. I'm setting them at 1% with Speedfan and they're audible but not annoying if you tolerate a bit of low pitched noise. At max, they're hurricanes. To be frank, I used the 4 of them at 100% to clean the dust from my pc and it even worked pretty well.
- They do a MASSIVE amount of vibrations. You can already feel the "punch" when you take one in your hands and use the finger to turn the rotor for a single "step", so to say. If you're thinking of using one or more of these, keep in mind that they need some serious dampening.
- The connector and pin-out is not standard so you have to re-crimp the connector, you can find the pin-out on the interwebz. The cable is also pretty short.
- They want for a lot of current, don't run these from a motherboard header. I personally use a PWM splitter that gets the signal from the motherboard and the current from a 8-pin that plugs directly into my PSU.
Other than that, the price for which I got them was tremendous. 13€ per fan from China shipping included from eBay, barely higher than the best prices you can find on Taobao. 4 fans came perfect, 2 have some slight balancing issues but are still useable. Absolutely impressed.