Initial 9.8.0 GA release for R500/R700 had issue ZF-7357: Not using 2-stream rate with Intel 7260 2x2 11ac NICs.
Firmware builds 188.8.131.52.101+ have the fix to improve performance for these clients.
Next 9.8 MR2 release is expected in Nov14. Not sure if 5G background scanning
will be enabled or disabled by default. If not enabled, running ChannelFly for a
period of time will allow your APs to decide on other than channel 149. Stopping
it after a period of running, was recommended to prevent problems in .106/.108