Zero,
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.
Thanks,