Well, before you start removing metal, have you tried using a good grease rather than oil on that part? It made a big difference for me.
I used some slide glide and slide glide lite. I think the lite worked better IMO.
The trigger pull basically has four parts as far as i can tell. the takeup that is mostly the trigger spring. Pushing up the FPS. Where the bent metal bit engages the sear, and moving of the sear.
between a buttload of dryfire with molly grease on parts that made contact (probably about 500-700 trigger pulls), removal and cleaning of striker, cleaning out of manufacturing grugne in the striker channel (was lots of plastic dust in there for some reason). I got it smoothed out a bit from box stock. There's stilla bit of gritty feeling that i believe is the FPB being pushed up the last little big while you start to engage the sear.
I think the FPB would benefit form a chamfer rather than a bevel, and a good polish. Jusding from the dryfire ith it coated in molly grease, the FPB rotates during use (deliberately or not i dont know). Which meand a bad hand "chamfering" via dremel might do bad things to the trigger pull.
Later I stoned the nubbin on the trigger bar to get rid of the rough spots form being stamped. This gave me smooth surfaces but a sharp corner, which didn';t work out so well. then polished the sharp corner off and that fixed it. takeup/pretravel is smoother and more even than before, but the "notch" where it picks up the load of the striker spring is still there.
According to other folks, with a stock glock striker spring (5.5lb) and a lighter trigger spring, they have gotten the trigger down to a bit under 4lbs.
*edit* went back and checked, using a stock glock striker spring cut down to the M&P length, they are lighting off ammo reliably and with a stock glock trigger spring and polishing, have the trigger down to about 3lb 10oz. *edit*
I have a stock glock spring on order to try out. I'm not going to try polishing the FPB without having a spare.