I haven't personally worked as a freelance copywriter, but have hired a few and I have a friend who did article writing for a while. As a buyer, I prefer a fixed rate per piece, disregarding word count, because quality is more important than quantity for my projects.
However, for the pseudo-seo, kinda-spammy-but-technically-not-but-actually-it-sort-of-is-spammy article generation industry, price per word is common. Probably more common is price per article with a fixed word length requirement - which boils down to price per word anyways.
So let's break down your full time job. You worked 40 hours per week and there's 4.34524 weeks in a month. So you worked about 174 hours each month. You mentioned the company you worked for was focused more on quantity, not quality, so I'm estimating you'd do a 300-word article per hour. (I'd love to know what your exact quotas were, if any.)
Using those numbers:
pricePerWord = EUR800 / (174 * 300) = EUR800 / 52200words = EUR0.0153 per word.
So for a 300 word article you were getting paid about EUR4.59, which lines up pretty well with the average rates you find on volume focused services like iWriter.
I imagine the trick to making this type of work profitable for the freelancer is in cutting down the time it takes to write an article while keeping the quality at an acceptable level to the client. If I get paid $5 per article and it takes me an hour to write it, that sucks. But if I get paid $5 per article and I can write 5 or six in an hour, that doesn't suck. Like I said I've never worked in the field, but I'd experiment with a combination of format templates for different article types that can fit any topic, and speech-to-text/voice recognition.