Turris 1.0 vs. Turris Omnia - Difference in 802.11ac performance

I have both Turris 1.0 and Turris Omnia. Both are behind UPC modem, each has its WAN socket connected into its own socket on UPC modem (Turris 1.0 and Turris Omnia has it’s own public IP address).

In my Turris 1.0 I have original 802.11ac miniPCI-e card from Omnia (WLE900VX) (3x3)
In my Turris Omnia Ihave 802.11ac miniPCI-e card WLE600VX (2x2)

Both routers are using same latest drivers and packages which were deployed by regular updates and are using the same configuration.

When I start downloading a large file (aprox. 5GB), It takes on Turris 1.0 aprox. 30 minutes but on Omnia it takes 10 minutes.

I wonder why there is such difference? Any ideas?

Are you downloading from the internet? If so, the cause can be the data analysis. Watch CPU utilisation during downloading.