I've had one idea from AMDave that seems very feasible. Never considered it before but it should be doable with some small changes and would eliminate the writes.

Instead of replicating the data from one drive to another, instead 'oscillate' the database connection from the webserver.

i.e.

still have two distinct databases on distinct drives as I currently have, but make them identical for all intents and purposes (I'd actually have a 3rd for static data which I've been considering anyway).

1. Run the stats update on db1, whilst the webserver points to db2.
2. On completion change the pointer from the webserver to point to db1.
3. Run the stats update on db2 (and ensure any changes include the ones to the prior update as well as any new), webserver still points to db1
4. on completion change pointer from the webserver to point to db2
5. Rinse and repeat.

It will mean I'll be duplicating some updates, but that's actually fairly minor.

Part 3 is the tricky part but is doable.

Might need a 3rd SSD in there perhaps.

Still need to think this out a little more.