R7000 with Shibby VS original FW - speed issues

Hello all,

I have just got myself connected to fiber to the home, at 1GB download.

running shibby 140 - I'm capped for download at 350mb.
Running latest stock FW - getting over 800mb.

wondering why? I have shut down everything on shibby FW (FW,monitoring,everything) and still.
is this a driver issue? why can't I max out download with the shibby FW?

thanks,
Uri