Physical NAND pages aren't really relevant. At least some high end SSDs I know of would gang multiple NAND chips together anyway and effectively the page size w

Physical NAND pages aren't really relevant. At least some high end SSDs I know of would gang multiple NAND chips together anyway and effectively the page size would be X*physical (where X might be 8 or 16). It could still do 512 byte writes well if it was configured that way. The limiting factor is the size of the forward map structures. To a lesser degree also things like garbage collection overheads and reverse map structures (particularly if you support deduplication or snapshots). But forward map is the main thing.