Uuna did a weapon ranking here: viewtopic.php?f=21&t=1113
This list is still valid and current. If you look, the difference between heroic Rathrak and heroic Vagaries is 124PP. Reaching the 3202 haste plateau is worth about 40PP, so you would want to continue using heroic Rathrak.
It's possible to get to 3202 haste with the heroic Rathrak:http://chardev.org/profile/400676-NLPriest.html
If you have access to heroic Rathrak, you have access to the rest of that gear, so not being at 3202 at the heroic level is just a temporary thing.
Also bear in mind that you can swap out the gloves and boots enchant for +50 haste enchants any time you want. And you are safe to swap out 2 red gems for 2 orange gems in your gear in order to get +50 haste there. Altogether you should have 150 points of haste available to you, should you find yourself needing more while working on gathering heroic gear.
Looking at this BIS list I put together, the haste is at 3288, so really you have 150+86=236 excess haste points avaialble on the way to BIS. So you should be able to reach it while keeping Rathrak equiped by the time you are halfway to full heroic gear.
* Try not to use the Robe of Glowing Stone as it forces you into using tier shoulders/gloves together, which both lack haste.
** The 25% nerf in DS affects boss
damage and health, so has no bearing on the damage you are doing.