both are good boards, and the ALiMagik1 (1647C) does catch up with the KT266A for once. so if your main concern is stability and compatibility, go for Magik, if you need that slight sped avantage (and the onboard RAID that comes with the A7V266-E) go for V266-E.
nothing much separates the two, compete well n all benches.
<font color=red>Nothing is fool-proof. Fools are Ingenious!</font color=red>