Like Ravyna said, it's probably not worth dropping much int for the haste if you need a lot of points to get there. But if you're extremely close, you should go for it.
Since 1% haste is 128.057 haste rating, .5% is 64.0285 and it's most likely not worth it.
You could figure out your actual DPS loss by using simcraft for your character's stat weights and then just do
DPS_Difference=64.0285*(Haste_Stat_Weight - Int_Stat_Weight). If the number is small enough for your liking, may as well go for it
Of course, if the haste stat weight is greater than that of intellect then it would be a DPS gain.