In general, a longer sight radius will get you tighter groups.
Longer barrels in the 1911 format tilt less than short barrels. Less tilt, less feeding problems. Seldom an issue once you get your feed ramp and your bullet shape to work well together.
Are the stock sights on the Range Officer adequate for Bullseye competition?
Dillon is good. If you are wanting to shoot large quantities of a single chambering (as bullseye shooters are wont to do) you would do well with a 550. A Square Deal might be even better (SD has autoadvance, where the 550 does not). 650 has case feeder options that (I think) the lesser Dillons do not. But don't neglect looking at the Hornady (or, if you are on a budget, the Lee Loadmaster).
Do you have experience loading already? Starting out on a progressive is not easy, but it is doable. If you take sufficient care will have no problems.
Good luck, Thanks for asking our advice.
Lost Sheep