The equation looks sound to me, although Vector rate (Ftck/bits in chain) will be approximate (actually lower) as most systems
have some 'housekeeping clocks' used between patter/vector shifts and update.
'scans per write' will depend on whether you can use an external write strobe (AutoWrite) - mostly only on high end controllers
so your figure will likely be 3 or 2.
'writes per location' will depend on flash type and whether or not you are using page buffers. Minimum without page buffers will
be 2.
BR
Barry