Well, when you get it, try it on the FS2000 and tell us all about it.
I'm thinking about a Trjicon ACOG as they don't need batteries and are always on. Really for my wife who, despite training, is slow and forgets stuff. Not good in an emergency situation where speed and accurate firepower is important. I need her to just snapshoot when the SHTF, not fumble with things.
I don't have that setup, but like Marrandy suggested . . . I too would be curious to find out the outcome with shooting the FS2K with that scope.
My setup is with a Trijicon 4X32 TA31ECOS with DOC optic for CQB. It's pretty sweet, but I never expected to shoot long range with the 2K, so I'm not too experienced with it.
As I understand the SIG 556 is pretty darn accurate, but compared to the FS2K, I wouldn't know, since I don't own one to do a firsthand comparison. It would be interesting to find out, since the SIG would have been my alternate choice if I'd never found a 2K in the right price range. Lucky for me I did! But do tell us what you find? I'd be very interested to read your result.