No changes that I'm aware of, other than I just ran a firmware upgrade on the MX67 in hopes it might fix things. (Without Success).
I have tested the following:
-PC hardwired to MX67 onsite = 100+mbs
-Hardwired to my local ISP router - 80-100mbs, wifi 50-60mbs
-Bypass site-to-site on Z3 and was able to pull 80-100mbs as well.