There really isn’t any ideal year for the CR80 because, from what I’ve read here before the engine went virtually unchanged from 1986-2003.
If that’s true, I’m guessing the reason for this was because, since the 80cc dirtbikes never competed in the professional ranks like the 125s and 250s (and subsequently, never in the media spotlight like the others), there was never a need to constantly update the 80 in order to stay competitive with rival brands, unlike their big brothers.
Now, whether the post-2003 CR85s are a significant advantage over the older CR80s, I have no idea. You’d have to refer to an expert who worked on these motors like Woltjer.
I’ve mentioned this many times before on the old site, I’ll never understand why they didn’t push for a stock, or near-stock in this case, 80 shifter class in addition to the 125s; something like that makes a lot more sense to me.