Riser question

[phluxx]

Hi.

New to BTC mining, and just spent the last couple of days milking a 6950 and 7870 for combined average 825M/hash.  It got me kind of addicted, so now I'm grabbing 4 more 58xx cards, but I'm not going to be able to fit them.  So, I have to use risers.  What happens to performance when you rise a 1x slot for a bitcoin mining card?  Do you just use a 1x-16x riser to plug a 16x pcie card into a 1x slot, and a 16x to 16x to just "extend" that slot so you have room to place the video card elsewhere?

Thanks.