The test is over. The M8 will start to be issued to Army units sometime in FY2005. It is chambered for 5.56mm. H&K's website has a pretty good section on all the particulars for this weapon. The primary sight system is optical, but back-up iron sights are mounted as well.
The 6.8mm Rem SPC was developed by Remington based on a request and input from USASOC and the AMU at Ft Benning. Dept. of the Army has made no formal decision on wide scale introduction of this round.
I completely agree with the Beretta M9 comment. Based on my experiences with the M9 (Including being hit in the head with a slide) I will not own Beretta ANYTHING. .45 is the way to go - why have 15 maybe's in a magazine when you can have 7 definitely's. Case in point: Most operators (both US and ally) carry .45's or .40S&W.