quicksync is superfast for me even with high compression settings, if i use x265(SW) its damn slow with 4 core...(better compression for sure but not feasible)
so
I use voukoder quicksync H265(HW) veryslow look ahead vbr which is really good but i asked question to myself can vouk add 3pass encoding for lesser file size? 
i guess ffmpeg support it
Here's how 2 pass works: encoder firstly run through the whole clip to get quality for each frame (or block in frame in more rencent encoders) called pass 1, then mass adjusts all the quality values to get the file size, called pass 2. Which your 3 pass doesn't make sense to me... (I might be wrong on this)
I'm not sure why you are targeting file size instead of quality for a project output though, and I don't think quicksync h265 is anywhere as good as official x265 (I maybe wrong on this too), maybe give a try on x264 in crf mode, it can be fast as well, and might give a better quality result
Here's how 2 pass works: encoder firstly run through the whole clip to get quality for each frame (or block in frame in more rencent encoders) called pass 1, then mass adjusts all the quality values to get the file size, called pass 2. Which your 3 pass doesn't make sense to me... (I might be wrong on this)
That is the classic approach you are describing here.
x264 for example supports multipass (or n-pass) where the 1st pass is doing what you described above... the other passes are just about fine tuning the data and the last pass is actually encoding the data. It could be even a 10 pass process (but mostly makes no sense).
btw. NVENC handles it differently: It does 2-pass encoding in actually 1 encoding pass. I just have to send the data once. Not sure about the details though.
I'm not sure why you are targeting file size instead of quality for a project output though
Fully agree. Filesizes, bitrates, etc only make sense if you are limited by the filesize of a physical media e.g. BluRay or USB drive. For YouTube and similar just think about quality (~ quantizer values) and find a good compromise between quality and upload speed)
But back to topic: I am not sure what the benefit of a 3-pass, 4-pass or even more is. I highly doubt the decrease of filesize would be that big.
only use crf.
