[opus] opusenc equivalent of lame presets

[Carsten Mattner]

Are there comparable presets or recommendations for opusenc
vbr parameters?

lame --preset standard --> opusenc ???
lame --preset extreme --> opusenc ???

I have used opusenc without custom vbr parameters and
the files were much smaller than for lame's standard preset
but I can't answer if that's comparable or the result was
lossier in opus. Hearing tests of course show no difference
but it's good to know before I encode routinely for avoiding
later surprises with more complex input.