hx750 vs ax860 vs ax860i?

Hi,

I recently built a new desktop. I really wanted a quiet computer, so I replaced all the fans to noctua's. After replacing, I could only hear my gpu and psu sound. However, I thought the hx750 would be very quiet, but it is a bit louder than I thought. So I thought I might switch to ax860 or ax860i depending on what other people say.



So my questions are below:

1. Could someone tell me the fan specs of each model and probably from experience how the noises differ?



2. I heard while hx and ax turn off their fan during low load, axi doesn't completely turn off. Is this true?



3. If I chose to upgrade, which one do you think between ax and axi is better?



Aside from quietness, I think the 860s are gonna be a bonus for my future dual gpu too. I use r9 290, which is a graphics card that consumes probably the most wattage right now. If I CF r9 290 on hx750, it might still run, but it's going to be full load all day and be really loud.



And the last question,

4. I bought hx750 for $130 and both ax and axi are $200 in Canada. Considering everything, do you think the upgrade is worth it?



Please give me an advice. Thanks!