Most 1911's don't have a rail machined into the slide to accommodate a red dot. Most Sigs and the Range Officer don't - at least to my knowledge. Are you planning on adding something to the stock gun for the sight? If not, I'd look to other models.
I ran a red dot on one of my Glocks and hated it. I actually shot better without it. I had a hard time being able to bring up the gun and find the dot quickly. That may have something to do with the amount of time I gave to get used to it (maybe 3 range trips) and my astigmatism. That being said I used a Primary Arms Micro and a Vortex Venom, both were solid sights.
Don't Tread On Me is what it says and I'll take that to my grave.