Let's see, I 've mounted a Leupold 1-4, an IOR M2, a gen2 Holosight, and an ELCAN on my DSA SA58 carbine using the DSA HD mount over the past couple years. Unless you remove the factory rear sight, I needed high rings for the Leupold and IOR. The ELCAN/gen 4 mount was OK with the rear sight as is. The problem I ran into with optics height (all 4) was cheek weld. I finally put a slip-on stock cover to correct for this low weld problem.
I didn't leave the Leupold on for long, as I didn't have the cheek piece yet and I had borrowed it from a deer gun (shotgun).
I didn't really like the IOR optic, although it seemed well-built, and the QD rings were quite nice. A pita to site in, poor directions, marginal eyerelief. The rubber scope guard sucks with glasses. Sold it for what I had in it. Some guys really like these; not me.
I really like the Holosight/Eotech, except for the ~short N battery life. Iron sights won't cowitness on the FAL. This optic I have used on several guns, including a slug gun. Currently on my AR10. Neat...
I replaced it with the ELCAN. Nice glass, but BIG. Good/decent eye relief for the .308, but I still ended up scratching my glasses with the rear sight when snugging into the ELCAN. Ended up selling this to buy another ACOG for a mousegun.
The other serious problem I had with the optics, however, was that I wasn't quite happy with maintaining zero. I at first thought the problem was with the IOR, but then my ELCAN wandered a bit. I think the multiple locking plates on the HD mount are better than nothing, but not by much. Still seemed to move a tiny bit on me.
I can shoot almost as well with the irons with my FAL as I can with a low power optic at the ranges I shoot. By this I mean ~3 MOA at 100 yds with milsurp from a bench. I could do closer to ~2-2.5 with optics. The plus side of removing the optics is that I'm once again back to a light, comfortable, easy-to-clean, fast-to-shoot rifle. The FAL stock and upper reciever just isn't properly designed for mounting optics, IMHO.
Your mileage may vary, and half the fun is trying stuff out. Enjoy!