I have a sapphire 5670 1gb on a ASrock M3A770DE, the mobo only supports 16/4 crossfire. As the 5670 is not that expensive i am considering to Xfire it as i've heard that 16/16, 8/8 and 16/4 do not strand too far in performance. Just checking if that is in fact true. Selling the 5670 and buying another single card isnt an option as used hardware in my town isn't easy to sell.
Do you guys think its worth it or the gain would be mininal? Tomshardware 2010 charts shows good performance gain for 5670x2 but i guess it was tested on a 16/16 mobo, so thats why i ask. I play my games at 1920 x 1080.
In PCI-E 2.0 motherboards,the difference between dual x16/x8 with x16x4 isn't much so you'll get a good boost in performance but I would recommend getting a single fast card over 2 5670s.(Such has HD 68xx/69xx series)
For 16/4 and 16/8, my understanding is 8/8 is negligible difference but 4/4 is a much more notable decrease. However, basically, the weaker the card the less crippled it is by the reduced speeds.
So, while 8/8 is very negligble for most cards, 2 x 5970s would lose out on noticable performance compared to 16/16 while the 5770 would likely not lose any performance.
Meanwhile, at 4/4 I would imagine cards like 5850 would be suffering similar to how the 5970 did with 8/8, yet at the same time, a card like 5670 I would expect to not be effected by 4/4 very much at all.
Understand this is hypothetical based on benchmarking of the bigger cards awhile back and so assumptions are being made rather than having any hard facts or benchmarking of the cards in question.
But ultimately the weaker the card, the slower/less information it can push through anyway, so slower lanes should have minimal impact as the card could not make use of fast lanes (in a similar way that new 6gb/s technology are of very little use currently for HDDs because HDDs haven't been able to saturate a 3gb/s sata, whereas SSDs were far more excited by the increase in speed)