Confused about pci-e risers

[brnkcv]

Hey, 

I'm just setting up my first rig and am confused about the cable risers.  I plan on using 4 r9 290x's with an asrock 990fx extreme 9.  Here are my questions:

1. Some people recommend 1x to 16x and some recommend 16x to 16x.  Is there a difference for practical purposes?  I figure there must be some difference but I have no idea what it is.

2. What is the minimum length the cables should be?  I can get a hold of plenty 19cm cables, but 28cm and 33cm are sold out.

[xocel]

In regards to #1: Depends on the slots on your motherboard. Mine has 3 16x slots and 3 1x slots so i would go with 3 1x to 16x and 3 16x to 16x. There's quite a bit of flexibility there( e.g you can use 1x to 16x risers in a 16x slot). I just like everything to match properly

Length of cable depends how/where you intend to mount the cards. I prefer to go with longer ones as too much cable can be worked with, not enough is a problem. 

Also if your planning on running 4+ cards i recommend getting the powered risers (with a molex plug) to avoid burning out pci bus etc.

[brnkcv]

I want to hang my GPUs high enough/far enough away that everything stays cool enough.

1. Is 19cm long enough for this purpose?

2. Is 19cm long enough to hang in the milk crate configuration?

3. If 19cm is too short,  can I connect two 19cm together? I've seen that this might be ok but I'm concerned that 24/7 use may be an issue for linked cables.

Thanks!