Note: I could just add "discard" to /etc/fstab, but wouldn't that wear out the SSD faster than periodic trimming?
I don't know precise numbers, but IME none of those made a difference performace-wise. I'd say if SSD wear is a problem (i.e. if you estimate it within expected usage time of the device), just switch to a HDD.
HTH,
Using discard will cause less wear than using fstrim or not using TRIM at all. TRIM gives the SSD more freedom to do wear levelling. Anyway, wear isn't an issue on anything but low quality hardware. Even the consumer class drives like Samsung's EVO line are going to take 5+ years to burn through the P/E cycles with extremely heavy usage. You can keep track via the SMART data. Samsung drives have an entry with the number of P/E cycles so far and the percentage of remaining life and other vendors probably have a similar field (but perhaps not with the same transparency).