Value of nSequence when it is less than FFFF FFFE

[NotATether]

So I am aware that in order to enable RBF, a transaction input must have an nSequence that is less than FFFF FFFF - 1 (in other words less than FFFF FFFE ), FFFF FFFF is the preferred one here because FFFF FFFE is used when you also want to make use of locktime.

But do any of the lower sequence values have any significance in the RBF transaction? Presumably, transaction replacement is governed by the transaction fee, so that one with a higher fee (as well as paying additional tx size * minrelayfee) replaces a lower one. But does the sequence number have any effect at all?

Meaning is an nSequence of 0 equivalent to FFFF 0000 and 0000 4000 and FFFF FFFD in this context?

I am also aware of this in BIP125:

Inherited signaling: Transactions that don't explicitly signal replaceability are replaceable under this policy for as long as any one of their ancestors signals replaceability and remains unconfirmed.

But it doesn't really answer my question.

[o_e_l_e_o]

But do any of the lower sequence values have any significance in the RBF transaction?

Lower nSequence values imply a relative timelock, as specified by BIP68.

Presumably, transaction replacement is governed by the transaction fee, so that one with a higher fee (as well as paying additional tx size * minrelayfee) replaces a lower one. But does the sequence number have any effect at all?

In terms of RBF, no. The nSequence number signals replaceability, but higher nSequence numbers are not prioritized over lower ones. It is based on fee alone.

Meaning is an nSequence of 0 equivalent to FFFF 0000 and 0000 4000 and FFFF FFFD in this context?

Strictly in terms of the RBF, it makes no difference. But it could make a difference if your replacement transaction includes a timelock which means it can not yet be mined.