when slot 1 is populated with a sound card / raid card / other
Slots 2 & 4 will use the NF200 and both run at full x16 speeds
HOWEVER, it has been proved that the lag of the NF200 chip negates any gains of running cards at x16
see this reviewhttp://www.tweaktown.com/articles/4147/nvidia_nf200_x16_x16_vs_intel_x8_x8_p67_performance_analysis/index1.html
i have the Z68 version of that board so the same goes, it just comes down to where the cards fit best.
I use slots 1 & 3