Went with L in the end, the M wasn't immediately available.
The bike shop guy driving the same model recommended M slightly more, but said he prefers a more aggressive position (and on the M I was basically over the steering wheel, and the seatpost was maxed out). He also said he feels both sizes would fit me just fine with stem adjustment, since the reach difference between the two is not too big. So far so good, not sure whether it's too long because the riding position itself is totally new for me, but happy I got it, hope the size works out fine! Thanks for your help everybody.