The HTML5 entities list and code, after cleaning out the dupes and other crap, still turns into >20k of binary (i.e. around 2/3 as big as everything else so far; which includes a HTML tokeniser/parser, DOM viewer, UI, and crude renderer)... the HTML4 ones are a slightly better ~4k.
Especially since it's not needed for Acid2 pass and would otherwise contribute to >30% of my 64k budget, I'll stay with the 253 HTML4 entities. It'll be easy to add the rest of them anyway.