I'm coming from Sigs also. My biggest stumbling block with the LEM right now is how far back it breaks. I tend to anticipate the break a little bit and push shots a little low. I also figured out that my P2k seems to have more of a drive the dot POA/POI on 15 yards and in targets which is adding to the problem. This is with non tritium stock 3 dots.
I'm less than 1,000 rounds into this though. I'm really digging the pistol so far. I'm debating going ahead and swapping sights as I intend on this being a long term commitment. Fiber Dawson's are looking like an option.