Now looking at those..... the Gskill goes out the window at 1600 as the 1866 is same price. I like the Mushkin 1866 better than the Gskill but for $19, I don't like it that much. Then again for $17 over the DDR3-1600 Mushkies, the Gskill 1866 may not be all that attractive either. At $10 more for the Mushkin 2133 over the Gskill 1866, I like that extra $10 investment better than the $17 jump from 1600 to 1833.
So in each category, ya gotta like the ones in bold. $27 for the jump from 1600 to 2133 makes a lil more sense than the $17 jump from 1600 to 1866 but I'd be hard pressed to say any of the bold ones is a bad decision.
Of course if ya shop around, you will likely find better deals and if ya look tomorrow, it could all switch up.