FCPX vs gtx 780 vs gtx 960.

Then I got the used gtx nvidia gforce 780, I didn't get the gtx 780ti because I couldn't find suitable prices, so I got a gtx 780, I installed it on the mac pro 2008 with the 2 6-pin cables and 8-pin put the nvidia driver and it works wonders.
But there is a problem, on the online benckmarks they say that 780 3gb is 40% faster than the gtx 960 4gb I had before, but in reality I tried with fcpx to export a 9 minute movie in 4k same clips same format but first with gtx 960 4gb and popi with the gtx780 3gb.
I was disappointed here are the results:
FCPX 10.4.6. rendering test on Mac Pro 3.1.

9 minute video in 3840x2160 25p. Apple pro res 422.

Gtx 960 4gb export time Minutes 5.58.

Gtx 780 3gb export time 6.48 minutes.

so the 780 took almost 1 minute longer ... but why?
shouldn't it be more powerful and faster than the gtx 960 4gb?
thank you.

JonnyK wrote: ... I got a gtx 780...But there is a problem, on the online benckmarks they say that 780 3gb is 40% faster than the gtx 960 4gb I had before, but in reality I tried with fcpx to export a 9 minute movie in 4k same clips same format but first with gtx 960 4gb and popi with the gtx780 3gb.
I was disappointed here are the results:
FCPX 10.4.6. rendering test on Mac Pro 3.1....the 780 took almost 1 minute longer ... but why?
shouldn't it be more powerful and faster than the gtx 960 4gb?...

If you are exporting to H264 or HEVC, the Xeon-powered Mac Pro 3,1 has no built-in hardware acceleration for video encoding. In theory nVidia has NVENC but that comes in various versions with different levels of software support. I tend to doubt FCP uses that, and am not sure Premiere or Resolve on a Mac Pro 3,1 uses NVENC from a GTX-780/960 either.

The performance numbers you mention are for GPU functions, not video decode/encode. The video acceleration logic on an AMD or nVidia GPU have little more in common with the traditional GPU functions than a ham sandwich. The video acceleration logic is a totally separate block using a totally separate API.

One easy experiment is fully render the timeline by doing CMD+A then CTRL+R, then export that. This helps distinguish between the render phase and encoding phase.

In general if you want faster export to H264 or HEVC you need a newer machine. Even a refurbished M1 Mac Mini would probably export that much faster: www.apple.com/shop/product/FGNT3LL/A/ref...8e8b29c7bf67192683f7

TOTAL disappointment the gtx 780 3gb with fcpx and with files in 4k converted to pro res 422 in the timeline proceeds with jerks and distorted audio while with the gtx 960 4gb it proceeded perfectly without problem and to think that the 960 is 40% less powerful than the gtx 780 !!!in my opinion the problem is the gb, 3gb are few for the 4k that's why the gtx 960 with 4gb works better, I threw away 150 euros for a gtx 780 USELESS, too bad.i will have to get a gtx 980!

Do you think that if I install a gtx 980 4gb I will have significant improvements with fcpx?
in fact, if with the gtx 960 4gb it works well then with a gtx 980 4gb it will work even better, am I right?
I don't care much for exporting the final movie, but I am interested in a smooth timeline and fast effects rendering with 4k files, thanks.

JonnyK wrote: Do you think that if I install a gtx 980 4gb I will have significant improvements with fcpx?... I am interested in a smooth timeline and fast effects rendering with 4k files, thanks.

Sorry, I don't know. The last Mac I had with an nVidia GPU was a 2013 iMac 27, which I sold long ago. 

You could download the free version of DaVinci Resolve and see if that works any better. OTOH even if it works, Apple is unlikely to update FCP for the sake of a 13-year-old machine. 

In general newer versions of MacOS and FCP work better with AMD GPUs, but I don't know which AMD GPU model is the best bet for FCP on a 2008 Mac Pro. Maybe somebody here with an old Mac Pro has tried it.

There were a lot of Metal performance optimizations in FCP 10.4.8 and later, but I think that requires Mojave.