That would all be an improvement to the current wording in my opinion.
I can understand your hesitation about some users perhaps not understanding 'optimal'.
(while technically very defendable: optimal file size vs. cpu burden)
Not strongly against it, but choosing something like 'small file size' for the FLAC preset suggests there will be a noticeable difference with the optimal/common setting.
No. it really won't.
Just try it out yourself. Encode a wav to flac with both -5 and -8 settings and see what it brings.
I just did that on a 10 min. track:
That's why I suggested a bland sounding 'custom'. It will be hard to find another word that is actually making much sense here.
But I do understand we can't cover all bases here, so for me 'smaller file size', 'common' etc. could be acceptable options, or perhaps slightly better: 'Recommended'. (which it actually is, when you do a web search on any forum/website that has a good understanding of the matter)
As long it isn't going to be 'archival', 'portable', 'jazz', 'classical', 'vocal', you won't hear me again about this.
(haha, sorry, couldn't help myself)