[CannondaleF9]

This is probably dumb, but I want to put a 45t 12 speed cassette on my hardtail instead of a 51t, even though I am running it 1x. I have an extra derailleur I could use for this bike, but it's the (1x) 12 speed, rather than the (2x) 12 speed derailleur.

So my question is, what matters more, the max gear rating (45 or 51t), or the cage length in the swing (SGS vs SGG)?

I have a feeling it's the latter, so I should use a 51t derailleur regardless, but a SGS is available online so I wanted to ask before ruling it out entirely.

 

[ToniT]

SGS is long cage designed for the 51t cassette, then you have a GS medium cage that was designed for 45t cassettes (but you can only get it as XT and XTR), how well the SGS works with a 45t cassette I don't know.
Hopefully someone else tried it.