300k words? Yes, you really need to know if there's a logistic error in chapter 2 on which the rest of the plot hinges before you've written that many.

Strictly speaking, we can't write at all without some internal editing, or we'd never string a coherent sentence together.

I find it hard to separate the thought processes of 'creating' and 'editing' in my mind. Totally unstructured creativity is what you do in a dream; the moment you use the precise tool of language to capture the dream, you must choose words and write with some grammatical discipline and descriptive accuracy to communicate it to a reader, i.e. 'internal editing'.

I can see why a novel speed-written in Nov will not feel 'ready' for review until it's been edited in Dec, but a second pair of eyes is almost certain to spot some issues that you're going to miss in the editing process.