1. Firewire is bustype 4, not bustype 3, my error above. So, my recommended 32KB restrictions would be on bustypes 4 and 7 (firewire and USB) not 3 and 7. Note also that 32KB is exactly the recommended buffer size for DVD reads due to the user data+EC data mixing algorithm (unless falling back to re-read bad sectors one at a time) so it's a good catch all mid-size and high-compatibility buffer size when dealing with optical drives.
2. An alignment mask of 3 means 4-byte aligned, not 8-byte aligned. Of course, there's nothing wrong with being more strict and until the most recent 13.1 code fix, the code was only 2-byte aligned so it needed fixing anyway. From past discussions with spoon, I believe he's now 4KB-aligned or 64KB-aligned all buffers, which covers all cases anyway and 64KB-aligned is especially good in order to avoid issues with chains that fail when transitioning 64KB boundaries.