R9 290 on a pcie 2.0 x4 slot - is the bottleneck really as high as people make it sound?

[Sauron]

So here I am wondering wether my trusty asus p8p67-m will let me down in a crossfire scenario. My first R9 290 is happily sitting in the top x16 slot, but eventually I was planning to get it a playmate and crossfire the hell out of them. Enter the pcie x16 slot with x4 wiring that is on the bottom of the motherboard. A lot of people, me included, usually discourage running crossfire in this scenario because of the bottleneck, HOWEVER... I found this graph online showing that a 7970 only looses about 4 to 5% of its performance to the lower bandwidth. Since the 290 is faster I'd assume bandwidth would be a slightly bigger problem, causing say an 8% loss. That would be entirely acceptable to me, do you think such predictions make sense or am I going to loose 30%+ performance?

 

This is the graph:

[Clyne]

YOU WILL HAVE A BOTTLENECK, get a new mobo with a x16/x8 or x10 speed which is better.

[Freaky_spider]

seeing as your first GPU will essentially be on Gen 2 x4 too, id expect maybe a 5-10% decreas from what you would get if youd have 2 gen 3 X16 slots

 

i wouldnt worry about it tho

[Sauron]

YOU WILL HAVE A BOTTLENECK, get a new mobo with a x16/x8 or x10 speed which is better.

 

I know I'll have one, but I don't want to change the motherboard for 10% extra performance. The question is not "will I have a bottleneck", the question is, will I loose too much performance for crossfire to make any sense?

[Clyne]

I know I'll have one, but I don't want to change the motherboard for 10% extra performance. The question is not "will I have a bottleneck", the question is, will I loose too much performance for crossfire to make any sense?

Then sell your mobo and use that cash to buy a new mobo that has x16/x8 or x10 speed, and you will lose performance if you do x16/x4 speed but i don't know if you lose too much because i haven't try it before. 

[harrynowl]

I know I'll have one, but I don't want to change the motherboard for 10% extra performance. The question is not "will I have a bottleneck", the question is, will I loose too much performance for crossfire to make any sense?

Well you'd lose a bit of the performance from both GPUs (I think they have to run at same bandwidth in xfire, idk it's not something that I've looked in to) but not worth buying a new board if you don't want to.

[Moldy]

Linus made a video on it back in the day:

Basically there isn't that much of a difference between x16 x16 and x16 x4.

[Sauron]

seeing as your first GPU will essentially be on Gen 2 x4 too, id expect maybe a 5-10% decreas from what you would get if youd have 2 gen 3 X16 slots

 

i wouldnt worry about it tho

 

Well you'd lose a bit of the performance from both GPUs (I think they have to run at same bandwidth in xfire, idk it's not something that I've looked in to) but not worth buying a new board if you don't want to.

 

Basically there isn't that much of a difference between x16 x16 and x16 x4.

 

Thank you all! That's exactly the info I was looking for. If I do end up doing the crossfire (the 4k display has the priority but I'll get it soon) I'll make sure to post some benchmarks on the forum!

 

 

Then sell your mobo and use that cash to buy a new mobo that has x16/x8 or x10 speed, and you will lose performance if you do x16/x4 speed but i don't know if you lose too much because i haven't try it before. 

 

As I said I'm not going to upgrade my outdated motherboard to another outdated motherboard for the sake of a little performance increase, but thanks anyway for the input