I've done most of my deer hunting for the last several years with an AR15 in 6.8 SPC. I can appreciate what you say about desiring a second shot without having to move to make it happen. I've made several doubles and triples with my 6.8. Made one last week on a pair of does.
I'd recommend it without hesitation for any person who hunted deer inside of 300 yards, period. Perfect caliber, and with a good barrel (mine's a Shilen) accuracy is world-class.
You could also look into an AR10 style rifle in .308 or, better yet, a 7mm-08.
The ONLY downside to hunting with a semi-auto is the fact that you have to deal with a bit of noise when loading the chamber. That can be mitigated.