I'm glad other people have said that they have this problem as a 2H Frost player. I do often find myself suddenly concentrating too much on my runes and RP at 35% to try and fit in a SR. It gets even more difficult when you have SR up and a Killing Machine proc, or you get SR up and use it a split second before Killing Machine procs and you lose the chance of a Killing Machine proc. I have done the same as what the OP has but on considerably more fights and I'm finding that my Obliterates not only do bigger crits, but generally I get more of them in on the last 35% than I do when solely gaming for SR on cooldown. In essence, I'm doing more damage in the last 35% but just sticking to my usual priority with Killing Machine procs. In a nutshell, SR makes no difference to my DPS, and is sometimes a loss, but the main difference being a rotation without SR being a lot smoother (at least for 2H, I haven't tried DW). As such, I just stick to my usual priority list and use Obliterate every time and ignore SR and I've never noticed a difference. So I'm sticking to what I'm most familiar with and what has the most natural flowing feel to it. Hope that helps.