FJ40INTOW,
I think that you will get so much more use and enjoyment out of your SR-556 as compared to your XD. Have you checked the safety selector on yours yet? Some people can rotate their selector past it's detent (with ease). If you experience this then it's not really that big of a deal. You can buy a new selector switch and drop it in for like 10 bucks. I guess some of the ones that Ruger installed, at the factory, were faulty.
Guys who call and ask Ruger about it are told this, "you have to send it in to Ruger to have it fixed." Most AR guys just laugh, hang up the phone and throw a new selector on theirs. It takes two minutes to do one.
I like mine. I have a pile of AR's. So, I have yet to shoot my Ruger. I can't seem to make up my mind on which optic to run. The SR-556 seems like it has a nice feel to it. Have fun trying to hide that monster Ruger box from your girlfriend/wife (or both).