Based on past experience
would say that reducing the number of renderers attached definitely
helps with performance. So, I'd say the solution which has the minimum
number of renderers attached would probably be the faster one.
One additional advantage with the "12 Month Renderers with Date Hash"
is that I'd expect performance to stay pretty constant, regardless of
how many dates need to be specially rendered. Rendering 20 cells or
100 cells, still only needs 12 renderers - maybe a little additional
time for DOM manipulation and date processing. If you were to attach
individual renderers, it would probably take a bad hit if your
requirements jumped from 20 to 100 cells.
If you do end up trying both alternatives, please do let us know which
turned out to be faster. I'd be interested.