Worse performance on 2Gb GTX680 than 1Gb 5770 in FCP

[upipes]

Hi guys,
I'm having a worse performance with a GTX580 with 2Gb DDR now in Mojave, than I had in El Capitan with a 5770 in Final Cut Pro. I find a better experience from 10.14.4 to 10.14.5,... but is still worse.
My setup is a MacPro 3,1 octacore 2,8ghz with 32Gb ddr, and the test I'm making is the known "BruceX test"
Is anybody experiencing something like me?
Anybody knows the issue or a fix?
Is this normal?

Timing:
El Capitan and 5770: 1 minute and 25 seconds
Mojave and GTX680: 2 minute and 55 seconds (10.14.4)
Mojave and GTX680: 2 minute and 25 seconds (10.14.5)

I'd appreciate your help. Thank you in advance.

 

[upipes]

Hi again,
Anyone with a GTX680 that can make a screenshot on system profile, exactly like the picture I'm enclosing, please?
I find a bit weird that those two lines about the nVidia card, tells that there are two: one with driver and the other one, no driver installed.
Any help it would be very welcome.

Thank you.