So, I’ve been talking about Haste like the calculation you want to determine how much Haste you need is 1.00 – (Desired Cast Time / Current Cast Time). It’s not. It’s (CCT/DCT) – 1. When I said that you needed 33% Haste to get to a 1.0s global cooldown, I was wrong. I was using the first calculation, 1 – (1.0/1.5), or 0.33. I should have been using the second, (1.5/1.0) – 1, or 0.5 – that’s 50% haste, and quite a bit harder to get to than I’ve been saying.
So, sorry for misleading you – mea culpa.
For the record, you already have 6% from Enlightenment, and another 25% from Borrowed Time. Haste percentages stack multiplicatively (Haste Rating is additive, and then you multiply the percentage you get from HR into the rest of the haste percentages you have), so between Enlightenment and Borrowed Time you get 32.5% haste. Since haste is multiplicative, you can divide your target haste (1.50) by the existing haste (1.325) to get the haste you need; that’s 1.132, or 13.2% haste from gear and buffs. That ends up being a little under 433 Haste Rating. That’s still eminently do-able, but not nearly as simple as I’d made it out to be.