Pete,
I wonder if you're perhaps getting confused by the terminology. AF ("Advanced Format") really means little more than that the drive uses *physical* 4KB sectors internally ... but that's nothing new; all large drives have been designed that way for many years now. The real issue is how the drive's interface presents those sectors logically to the outside world--that is, Windows or the host interface.
Don't confuse the physical sector size with the logical sector size. Most AF drives use a 512e interface, whereby the drive presents one physical 4KB sector to the outside world as a block of eight logical 512-byte sectors. The term "AF" by itself doesn't indicate what size logical sectors you're talking about, so it's more common to differentiate them as 4Kn ("native 4KB logical sectors") vs. 512e ("emulated 512-byte logical sectors"). In 4Kn, 1 physical sector = 1 logical sector. In 512e, 1 physical sector = 8 logical sectors.
Windows 7 has no trouble supporting 512e AF drives because to it they look just like the older drives with 512-byte physical sectors. AFAIK, Win7 does not support 4Kn AF drives, though. (See chart at the bottom of this
KB982018 article.) Windows 8 and 10 do, but I don't believe you can use a 4Kn drive with Win7. (That is, unless it's as an external USB drive--but in that case the USB interface is responsible for the 4Kn support, not Win7 itself.)
I suspect your research has been clouded by discussions around the issue of partition alignment.
Typical NTFS clusters or allocation units are 4KB in size, so even on traditional HDDs Windows is reading and writing 8 512-byte sectors at a time, whether or not it needs all 8. That's great on an AF drive, where it can correspond with one physical sector--whether that be one 4Kn sector or 8 512e sectors--provided that those 512e sectors correspond exactly with one physical sector. That's the whole argument for alignment; if Windows reads/writes 8 512-byte sectors at a time, and those 8 512e sectors line up over portions of two different AF 4KB physical sectors, that would reduce performance substantially. Performance is much better if those 8 512e sectors align with a single physical AF 4KB sector.
FWIW, I would think for compatibility reasons your SSD might use a 512e interface. If you can't find it specified in the SSD's documentation, you can check by running the command "fsutil fsinfo ntfsinfo x:" (where x: is a NTFS partition on the SSD) from a Windows command prompt. (That's easier to do with a desktop vs. a laptop because you can mount both the existing Windows hard disk and the SSD at the same time. On a laptop where you may only be able to install one disk internally at a time, you may need to actually install Windows on the SSD first.) That command will tell you what logical sector size is in use on that disk.
The bottom line is you don't tell Windows what sector size to use. You have some control over alignment, but not sector size, so don't worry about it. That's determined by the drive interface, and Windows will format the file system based on what the drive tells it to use. Windows will format the file system with 4KB allocation units, whether that be 8 512e logical sectors or (as supported by Win8/10) one 4Kn logical sector, but it's up to the drive to tell Windows whether it's 512e or 4Kn.
You do have control over alignment, so let Win7 create your partitions or use a third-party partitioning tool that will create properly aligned partitions.
