You can get Trijicon ACOGs from 1.5X all the way up to 6X depending on what distances you think you're going to be doing most of your shooting at.
Another option if you like the 1X CQB style sights is an EOTECH or an Aimpoint with a corresponding magnifier. This nice thing about this kind of setup is you can fund the 1X sight, and then come back later and buy the magnifier. They are not inexpensive, but this is one area where I feel like you get what you pay for. If you are thinking about taking your rifle into harms way then I would save for the best equipment I could afford that would be dependable. That might be a good set of irons for some people or an EOTECH with magnifier for others.
I also agree with JD about getting backup irons, either flip-up style or a fixed style that you co-witness with your optic. The rifle I am plotting out right now will probably have a fixed BUIS by Larue Tactical & an EOTECH 557.
This is the EOTECH with the EOTECH 3.5X Magnifier. It is on a quick transition, flip-to-the-side mount.
Here is the Aimpoint with the Aimpoint 3X magnifier:
Larue Tactical BUIS QD LT-103: