Few questions about pci risers

[pikuchato]

I did read some information but I just want to make sure I got it right before I actually buy it..

I currently have 2 Sapphire R9 290 21227-00-40G cards mounted on a Gigabyte GA-870A-UD3 mother board.
I am going to buy another 2 cards : Sapphire Radeon R9 290 BF4 21227-00-50G.

What I understood about pci risers is:
1) For those cards I have to buy risers with electricity.
2) The riser itself provides power only while the data goes thru USB connection (USB 3 is preferred for that reason).
3) The only difference between 1X16 and 16X16 is more power from the motherboard, When buying a PCI riser with electricity connection it doesn't really matter (1X16 or 16X16).

Please correct me if I'm wrong, I suspect number 3
Those cards will be powered by a different PSU (1 PSU for the system + 2 cards on motherboard and one PSU for the 2 cards with risers).

Did I get it right?
Thank you 

[pikuchato]

please? 

[prolom]

What are you currently getting from the cards that you have?

I kind of think it depends on the motherboard and a lot of other details.

I'll get my risers tomorrow so I'll try to comment.

[pikuchato]

I have an external fan and I'm getting ~820 per card with 40%-70% fan speed, can't stand the noise for more then 70% fan speed
 
Anyway I just bought this:
http://www.ebay.com/itm/171246370887

[Minerist]

1. Yes.
2. Wrong.
3. Wrong, but 1x riser is enough for mining.