Let's see if my bad english can help you.
Better source is the bluray iso, dvd, normaly 24 to 30 GB.
- When you encode from this source you can use 900 2 pass medium (slow would be better) for quality with the small file.
- 1500 2 pass medium (again if can use slow) for good quality
- 18 CRF if you really like the movie, size gonna be high but the best quality space;
- 22 CRF for good quality with small size;
- 24 CRF best smalll size with quality, above this you lose quality beyond aceptable, for me;
When the source is a reencode release with 8 to 14 gb you already lose some quality, aply same thing above.
Releases (torrents) with low birtrate are very carefull planned, thats why they have good quality with small size. When you reencode from this you will lose even more quality, soo in this case use 1000 2 pass medium for small or 1500 2 pass medium. CRF in this cases preserve almost always same size.
Always use slow if you have a i7, use 2 pass to obtain small size files. Soo, 40 minutes 5.1 audio can have 250mb for good quality and 350mb for better. Something between 600 to 900 according with the episode.
CRF gonna be according what you would like in terms of quality, in case of lots of change, movement, you will end up with big size files.
If the source is with too much noise you gonna need aply a filter, theres two:
NLMeans : very slow with very good result.
hqdn3d : very fast but great lost of quality.
I use Light NLMeans for very noise film / ultralight for a small noise film
And when the movie is heavly noise i use hqdn3d medium.
You need get lost of the noise, noise make you file size big without quality. But when you aply a filter you lose quality, soo you don't want a movie with 0 noise because gonna look artificial. You gonna use on animes like because noise filter gonna make even better them the original.
Audio 5.1 use 192 for shows and 256 for movies and if you really like the sound quality, or the movie, go for 640 AAC.
A tip for time, size and quality, encode only 1 or 10 minutes to preview the most close size and the quality as too know how much time gonna take to encode. That way you always gonna know best setting for a movie.
The movies that i just want to watch i encode on 1000 or 1500 1 pass medium, the ones i like i try keep the size between 2,5gb to 5gb because i always gonna watch again.
Low them 720p x265 do a bad job, it's really bad, i dont recommed, except for animated he can correct noise animes and make it really good. Done this to a pink panther with 70 mb episode very noise and got a ver clear 23mb. But becareful too much denoise you gonna get ghosts, NLMeans medium source animated is good.
Hope to help with this horrible english, it's not perfect but it's a way to evolve from in some direction.