I can concur with some of the above.
Back of MD11/DC10 or MD80/90 is terrible - not only do you get the usual swaying, it feels exacerbated by having all the thrust there. Also, the noise is terrible. I'm not surprised 1st is better (not been in 1st on these a/c) but you're further away from the engines!!
On the plus side, the 2/4/2 (? 2/5/2 some carriers) on MD11 or even better the 2/3 on MD80 is awesome in Y, b/c the plane needs to be over 80% full to start filling the middle seasts. On long distance, getting the 2 is awesome, especially if you're travelling as a couple. Getting the 4 or 5, not so much.